Interleukin 10 (IL10) is a poor prognostic marker in several cancers. Its role in breast cancer is not well elucidated. The present study is designed to see the expression of IL10 in breast cancer tissue and to evaluate its correlation with the established markers of prognosis. Sixty female patients who underwent surgery for breast cancer were enrolled for the study. Immediately after surgery, 2-5 g of tumour tissue and similar volume of peritumoural normal breast tissue were collected for IL10 assay. IL10 expression was assayed by immunohistochemistry. IL10 expressing tumours and IL10 non expressing tumours were compared. Chi square/Fisher exact test and student's t test were used to compare the data. p-valueless than 0.05 was considered as statistically significant. Thirty six patients (60 %) of carcinoma breast showed IL 10 expression in tumour tissue as compared to no IL 10 expression in any peritumouralnormal breast tissue (p < 0.01). IL10 expression had statistically significant correlation with locally advanced disease, tumour grade, HER2 + ve tumours and ER-ve, PR-ve, HER2 + ve breast cancer subtypes (p = 0.001, 0.001, 0.001 and 0.01 respectively). No correlation could be found with patient's age, tumour size, tumour histology and ER and PR status. Correlation of IL10 expressing tumours with several established poor prognostic markers of breast cancer may indicate the possible association of IL10 expression with poor prognosis. Large studies with long term follow up are needed to substantiate the association of IL10 with poor prognosis.