Objective: To investigate the inhibitory effects of RNAi (RNA interference, RNAi) expression vector on CXCR4expression in prostate carcinoma cell lines. Methods: Small interference RNA (siRNA) expression vectors for CXCR4 gene were constructed and transfected into prostate carcinoma cell lines(PC-3m and LNCaP)with liposomes. The expression of CXCR4 was detected by RT-PCR and western blot. Results: The expression of CXCR4 mRNA and protein in the PC-3m and LNCaP cells was reduced by RNAi expression vectors. The inhibitory rate of CXCR4 mRNA expression in the PC-3m cells was 87.81％ ± 10.20％ ,56.10％ ± 9.32％at the 24th hour and the 48th hour, compared with 56.93％ ±8.78％ ,49.24％ ± 11.23％ in LNCaP cells. The inhibitory rate of the expression of CXCR4 protein was 64.71％ ± 6.68％ ,58.66％ ± 11.56％ respectively. Conclusion: The expression of CXCR4 gene can effectively he inhibited by RNAi expression vectors.