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Introduction: Fletcher defines Round cell tumors as a heterogeneous, highly aggressive malignant tumors featuring primitive, small and monotonous undifferentiated morphology with increased N: C ratio. They mostly occur in children, adolescents and young adults and can occur anywhere in the body and differential diagnosis is particularly difficult due to their undifferentiated features. Increase in the burden of cancers including the round cell tumors has make it necessary for the need to diagnose accurately and also to determine the magnitude of the problem. Aims and objective: To find out the prevalence of round cell tumor in a pediatric cancer patient coming to Dr B Borooah Cancer Institute, Guwahati, To make the list of differential diagnosis possibility based on histopathology and To see the results of immunohistochemistry. Methods: It was a retrospective study from July2014-june2019. All cases reported as round cell tumors till the age of 18 yrs were collected from the records of pathology department. 148 cases were selected. Medical history was obtained from the patient's files: clinical examination, age at diagnosis, gender, location and histological findings. Paraffin blocks were retrieved and reviewed. Histological sections were routinely stained with hematoxylin and eosin stains. immunohistochemistry (IHC) was repeated whenever necessary. Results: The most common pediatric round cell tumors in Dr B Borooah Cancer Institute, Guwahati is Ewing Sarcoma/PNET followed in descending order by Non Hodgkin Lymphoma > Hodgkin Lymphoma > Rhabdomyosarcoma > Neuroblastoma > Myeloid sarcoma > Neuroendocrine tumor > Wilm's tumor = Poorly differentiated > Synovial Sarcoma = Rhabdoid tumor of kidney. Male predominate female (M: F ratio = 1.2: 1) in overall round cell tumors. Conclusions: There were significant overlap in morphology of the small round cell tumors, but careful search of the detailed history, location of tumor and presentations with imaging findings helped us to come to a probable diagnosis. Though IHC is indispensible and a very important routine accessory tool in making a diagnosis of small round cell tumor, the conclusion must be made knowing the fact that there is no antibody exclusively specific for a particular tumor entity and there could be cross-reactivity among various tumors. Interpretation of IHC results is not simply the description of positive or negative stains. Therefore, the conventional H&E morphology of the tumor in addition to the characteristics of each antibody, and the expression pattern of each targeted antigens must be considered. [ABSTRACT FROM AUTHOR]