We investigated the effects of Stattic, an important signal transducer and activator of transcription 3 (STAT3) inhibitor, on enhancing the anti-proliferative and apoptotic effects of docetaxel in lung A549 and prostate cancer DU145 cells. Cell proliferation, cellular apoptosis and expression of STAT3 target genes were evaluated by DAPI staining, Annexin V/PI staining, cell cycle analysis and Real Time PCR. The anticancer effects of docetaxel and Stattic combination therapy induced synergistic effects in A549 and DU145 cells with combination indices of 0.71 and 0.52, respectively. Annexin V/PI demonstrated that there was a 2-fold increase in the proportion of apoptotic cells in cells treated with docetaxel and Stattic in A549 and DU145 cell lines, compared with control groups. Compared with cells treated with either docetaxel or Stattic alone, the results of the current study identified a significant decrease in the transcript levels of the anti-apoptotic proteins Bcl-2 and Bcl-xl and a marked increase in the level of the pro-apoptotic protein, Bax in cells that underwent combination therapy with docetaxel and Stattic combination (P < 0.05). These results suggest that combination of a STAT3 inhibitor and taxan derivatives may be developed as a promising therapeutic strategy to treat patients with lung and prostate cancer.