BACKGROUND Adipose derived stem cells (ASCs) provoke the accumulation and expansion of regulatory T cells, leading to the modulation of immune responses in tumor microenvironment. OBJECTIVE To assess the effect of tumoral ASCs on the trend of regulatory T cells differentiation. METHODS Peripheral blood naïve CD4+ T cells were co-cultured with ASCs derived from breast cancer or normal breast tissues. In separate cultures peripheral blood naïve CD4+ T cells were exposed to the culture supernatants of ASCs. RESULTS Generation of CD4+CD25+Foxp3+ and CD4+CD25-Foxp3+ Treg subsets was observed after coculture of naïve CD4+ T cell with either ASCs or the related supernatant. The percentage of CD4+CD25+Foxp3+ cells increased after exposing naïve CD4+ T cells to both ASCs and their supernatants while augmentation of CD4+CD25-Foxp3+ subset mostly depended on the presence of ASCs. Similarly, upregulation of FoxP3 molecule was more significant in condition of cell to cell contact. IL-4 and IL-10 were up-regulated in the cocultured naïve CD4+ T cells after exposure to ASCs/supernatant while IFN-γ was down-regulated in the presence of ASCs. CONCLUSION ASC may act as one of the major players in tumor site with immunomodulatory effects, which may mostly be carried out through direct cell-cell interaction.