BACKGROUND: The Id2 gene is an endogenous negative regulator of basic helix-loop-helix factor, which is involved in the cell proliferation, differentiation and existence. Id2 also shows functional diversity in the progression and infiltration of different types of tumors OBJECTIVE: To observe the changes of proliferation and invasiveness of PC-3 human prostate cancer stem cells after shRNA-Id2 transfection. METHODS: PC-3 human prostate cancer stem cells in logarithmic growth phase were harvested to isolate tumor stem cell spheres by serum-free suspension culture. The expression of CD44+CD24-on the surface of tumor stem cells was detected by flow cytometry. The shRNA-Id2 expression vector was constructed and transfected into PC-3 human prostate cancer stem cells. Untransfected PC-3 human prostate cancer stem cells were used as control. At 48 hours after transfection, the expression of Id2 gene and protein in shRNA-Id2 transfected prostate cancer stem cells, NC-shRNA empty vector transfected prostate cancer stem cells and untransfected prostate cancer stem cells were detected by RT-PCR and western blot, respectively. The proliferation and invasion of shRNA-Id2 transfected prostate cancer stem cells and untransfected prostate cancer stem cells were detected by MTT assay and Transwell chamber, respectively. The expressions of E-cadherin, vimentin and Twist were detected by western blot and RT-PCR. RESULTS AND CONCLUSION: Tumor stem cell spheres were successfully isolated by the serum-free suspension culture. The expression rate of CD44+CD24-on the surface of the third-generation PC-3 human prostate cancer stem cells was (85.69±8.96) ％, indicating that the cultured tumor stem cell spheres overexpressed the phenotype of tumor stem cells. At 48 hours after transfection, the expression of Id2 gene and protein was significantly lower in the shRNA-Id2 transfection group than the non-transfection group (P < 0.05) , indicating that the expression of Id2 was successfully interfered with the expression of PC-3 prostate cancer stem cells. The invasive ability of the cells in the shRNA-Id2 transfection group was significantly lower than that in the non-transfection group (P < 0.05). Western blot and RT-PCR detection showed that the expression of E-cadherin, an epithelial marker of PC-3 prostate cancer stem cells, in the shRNA-Id2 transfection group was significantly higher than that in non-transfection group (P < 0.05) , while the expression of vimentin, a marker of mesenchymal stem cells, and Twist, a transcription factor regulating cell-mesenchymal transformation, in the shRNA-Id2 transfection group was significantly lower than that in the non-transfection group (P < 0.05). These findings indicate that RNA interference with Id2 gene can inhibit the proliferation and invasion of PC-3 prostate cancer stem cells by regulating the expression of E-cadherin, vimentin and Twist.