Introduction One of the important fields of comparative literature is the interdisciplinary studies such as psychological criticism of literary works. This criticism expresses and compares the states of mind and personality structure of artists of different countries with different cultures. Among the important subjects in this criticism is the archetypal criticism which looks at similarities and differences of literary works of different countries through an introspective and psychological view. In this regard, one of the important archetypes is the shadow archetype. This archetype is the animal and inferior part of human personality which includes all unethical, lustful and forbidden desires and activities. According to Young's theory, within the evolution and individualation process and in movement from shadow toward oneself, the ego should be able to pass the negative specifications of shadow such as pride, lust, greed, covetousness and etc. in order to reach himself. However, the shadow archetype has also positive aspect. Excitement, creativity, creation and many of natural instincts are positive aspects of shadow which the human needs them for life continuation. Whereas, when the poets sing the poem, they are connected to the unconscious mind and represent its contents to the audiences, investigation of archetypes such as shadow archetype is a way to recognize the hidden dimensions of their personalities. In this article, the poems of two poets, Forough Farokhzad and Sylvia Plath, have been investigated and discussed from this viewpoint. Many similarities and little differences of personality and lifestyle of these two poets led to occurrence of similar manifestations of shadow archetype in their poems. Methodology This research has been formed based on American school of comparative literature. This school believes that the similarities of literary works are raised from the common human spirit. In this research, author has investigated and compared the shadow archetype in the poems of Forough Farokhzad and Sylvia Plath by an analytical and descriptive method. The author, by library method and analysis of motifs such as love, pleasure, disappointment, idealism and thinking about death which are the aspects of shadow archetype, has come to this conclusion that the poems of these two poets, although in the same time period but with far distance and unawareness of each others, have various similarities solely based on the common human spirit. Discussion In this article, the manifestations of shadow archetype are investigated and compared in the poems of Forough Farokhzad and Sylvia Plath. These two poets sang the poems approximately within the same time period but in different geographies. Forough Farokhzad is one of the pioneers of Nimaeian Poetry (modern poetry) and one of the first famous persons of modernism in Iranian poetry. Living in a male-dominated society and experience of weak and unstable emotional relations have given a special courage to Forough so that she, in addition to break the old poetic frames, casts doubt on old laws and traditions of life. Sylvia Plath is an american poet and writer who is one of the leading woman in american literature for singing the confessional poem. Bitter and hard life style of Sylvia in family and strict and male-dominated society is evident in each line of her writings. These two poets, probably due to the extreme feeling of guilty, have unconsciously followed the shadow archetype in their books. Sometimes, they have used the word of shadow directly and sometimes indirectly as a bird or woman with an ambiguous and fictitious face. Investigation and comparison of these aspects is a way toward the unconscious inside of these two poets and also show the social and cultural similarities and differences in Iranian and American society during living and singing of these two poets. Conclusion Investigation and comparison of shadow archetype in the poems of Farokhzad and Plath not only show the hidden angles of their personalities but also represent the space of their family and society to some extent. Lack of affection in childhood and, more important, an unsuccessful marriage, caused that the said both poets always wish the love and affection. This point led to plenty use of shadow in their poetries in the concepts of lust and hedonism. Lack of sympathy, experience of violence and also frequent social failures represent another face of shadow archetype namely sadness and sorrow with this difference that the sadness and sorrow of the Forough in her first poetic duration are the sadness and sorrow of a young and emotional girl and it took a while for Forough to express the human deep sorrow. But Sylvia Plath tied her personal sorrow with human sorrow in her first poems with mythological and symbolic language. Shadow in the concept of nullity and disappointment has been used very much in the poems of two poets which rose from their failures and frustrations. Shadow archetype as the symbol of humiliation and disability has different usage in the poems of Farokhzad and Plath. Feeling of humiliation in Forough's poem is a result of an Iranian literary tradition namely the obeisance of loving poet against the beloved but the feeling of humiliation in the poem and prose of Sylvia is very deep and indicates one personality specification. Other aspects of this archetype such as fear, anger and violence are more obvious in Sylvia's poems. This issue although indicates her approximate extroversion in comparison with Forough but represents her harsher family and society space. Generally, Sylvia Plath, with using more aspects of shadow archetype, achieves complete cognition of that archetype and reconciles with that better. However, in Forough's poem, the active aspects of shadow archetype are less used. This point not only shows the approximate stillness and calmness of Forough's life in comparison with Sylvia but also it can represent the inherent and introverted modesty of the eastern poet. This issue caused that the Forough Farokhzad, in despite of plenty attempts, is not successful in reconciling with shadow and a kind of ambiguity, restlessness and anxiety encompass her life and poem. [ABSTRACT FROM AUTHOR]