Prostate cancer is part of male reproductive system cancers that causes of cancer related death. Although, multiple strategies have been developed, prostate cancer continue to represent a significant disease in globally. To overcome this problem, a deeper understanding of molecular mechanism that drive prostate cancer proliferation and metastasis to develop effective cure. In the current study, we investigate the signal transducer and activator of transcription 3 (STAT3) as oncogene that implicated in prostate cancer progression. Our results show a substantial level of STAT3 in DU145 and LNCaP cells. Furthermore, we show that chemo-preventing of STAT3 by resveratrol treatment or knockout of STAT3 expression in prostate cancer cells (DU145 and LNCaP) decrease cell viability. Resveratrol at different concentration show an antiproliferative activity against prostate cancer cells (DU145 and LNCaP), with most activity accompanied with 50 µM. For the first time in our lab, using CRISPR Cas9 technology to delete STAT3 gene to showed a significant reduces cell viability of DU145 and LNCaP, furthermore, the colony formation of both cells was inhibited. Interestingly, resveratrol follows the same trend as knockout of STAT3 by ameliorating DU145 and LNCaP viability and colony formation. Furthermore, Western blotting analysis showed that resveratrol inhibits STAT3 expression in both DU145 and LNCaP. These data indicate that STAT3 mediates prostate cancer progression. Inhibition of STAT3 by resveratrol mitigates prostate cancer activity progression.