Objective To investigate the relationship between STAT3 activity and sensitivity to cisplatin in prostate cancer cell lines. MethodsSTAT3 activity was examined by immunocytochemistry and Western blotting analysis in three prostate cancer cell lines: LNCaP, PC3 and DU145. Androgen-independent cell lines PC3 and DU145 were selected to examine the inhibitory effect of various concentrations of cisplatin (2 ng/ml, 20 ng/ml, 200 ng/ml, 2 μg/ml and 20 μg/ml). STAT3 activity of DU145 cell line was re-examined by Western blotting analysis after treatment with low concentration of cisplatin. ResultsThe STAT3 activity of androgen-independent cell lines PC3 and DU145 was higher than that of androgen-dependent cell line LNCaP. The sensitivity of DU145 cells to cisplatin was lower than that of PC3 cells with lower STAT3 activity. Treatment with low concentration of cisplatin for a long period caused STAT3 activation in DU145. ConclusionOur results suggest that STAT3 may play a role in regulating the sensitivity of prostate cancer cells to cisplatin.