A lot of misunderstandings occur within Indonesians studying Japanese regarding the manners in verbal forms, for example the use of keigo (honorifics). Keigo consists of sonkeigo (honorifics to raise the position of the interlocutor), kenjougo (honorifics that lower ourselves ), and teineigo (regular honorifics by using desu/masu). When learners write business letters in Japanese, they use manners in written forms. The usage of verbal forms when writing is a mistake. Opinions like this aren't exactly correct because writing letters in Japanese is not the same as writing a scientific article that uses written forms.On the other hand, the culture of uchi (in-groups) and soto (out-groups) have impacts on the use of language. Different from Bahasa Indonesia, writing letters in Japanese is heavily influenced by the culture of uchiand sotothat will affect the diction in the business letters. When writing letters to people and companies who are soto, then keigo and some special phrases should be used. There are different words and phrases used when talking about people included in the uchi to the other person who is considered as soto. This is a characteristic in Japanese language. The reason for this research is to understand how applications of the culture of uchiand soto in Japanese letters, specifically Japanese business email. This research uses the descriptive qualitative methode. The technique used to gather data is through literature review. The source of data is from documents of letters and textbooks from the Tegami no Kakikata (correspondency in Japanese) and BijinesuNihongo(Japanese for Business) course.Based on the data analyzed it is known that we can determine that there are some similarities and differences in a Japanese business email. The similarities are that both letters use the formal form for uchi and soto and have a clear purpose. While the differences are that in the email for uchi a long formal opening, body, and closing text is not needed. In addition, being too formal is not needed like in the soto letter, they also have special phrases used in both emails. This research is shown that soto emails, in the beginning the receiver's name is written in full, their position, as well as the name of the company which, in Japan, is written in reverse. Howefer letters for uchi1 writes the name as Yamamoto San orKatouBuchou, this is not allowes when writing emails for soto. Emails for soto should first mention the department and then the name of the receiver, Yamamoto sama or KikakubuchouKatousama. When speaking to someone who is a soto regarding someone who is a uchi, they would normally not use keigo. Email addressed to uchi within the company whether it was to a superior or a subordinate, the opening will use otsukaresamadesu . However the above email for soto writes with the opening itsumoosewaninatteorimasu .