OBJECTIVE Curcumin is the major component of the spice turmeric and the yellow pigment in curry powder. Many studies have shown that curcumin (diferuloylmethane) has significant antiproliferative and apoptotic effects in cancer cells by several mechanisms. Signal transducers and activators of transcription (STAT) proteins are critical in mediating a response in hematopoietic cells. This study was designed to investigate whether curcumin is associated with proteins involved in signal transduction and activation of transcription (STAT) and to investigate the expression of signal transducers and activators of transcription and the significance of the STAT5 signalingpathway of by treating k562 cells and cells from CML patients with curcumin.METHODS The study was divided into the following groups: normal control cells (human bone marrow cells), untreated K562 cells, curcumin treated K562 cells, IFN-γ treated K562 cells, curcumin plus IFN-γ treated K562cells, and CML patient cells with and without curcumin treatment. Cell proliferation was measured by the MTT assay. The expression of STAT5 mRNA was determined by RT-PCR. The expression of the STAT5 protein was assayed by West-blotting and the expression of STAT5 in K562 cells was examined under confocal laser-scanning microscopy. The expression of STAT5 mRNA of K562 cells was determined with in situ hybridization. EMSA was used to assess the change in binding of STAT5 with DNA in CML patient cells.RESULTS The proliferation of the K562 cells and CML primary cells was decreased in the curcumin-treated group and/or IFN-γ group. The expression of STAT5 mRNA and protein were decreased the curcumin-treated group as compared with the K562 untreated group (P＜0.01). STAT5 mRNA and protein expression was decreased in the IFN-γ group compared to the untreated K562 group (P＜0.01). Combined use of curcumin with IFN-γ inhibited the proliferation of K562 cells and decreased the expression of STAT5mRNA and protein of the K562 cells. For the CML patient cells, the OD value of STAT5-DNA binding in the curcumin treated cells was less than that compared to untreated cells.CONCLUSION The antiproliferation effects of curcumin may partly be mediated through signal transduction and activation of transcription and may involve the STAT5 signaling pathway.