Abstract: Objective: To investigate the feasibility of the folate-modified fifth generation polyamido-amine dendrimer (G5-PAMAM-D-fol) as a gene vector in the suicide gene therapy of prostate cancer. Methods:G5-PAMAM-D-fol was used as the gene vector to transfect the recombinant plasmid pcDNA 3-tk containing the HSV-TK suicide gene into the prostate cancer cell lines PC-3 and LNCaP. RT-PCR assay was used to detect HSV-TK mRNA expression in the two cells lines24 hours after transfection. After another 24hours, the prodrug ganciclovir (GCV) was given to the transfected PC- 3 and LN-CaP cells at different concentrations. MTT assay was carried out to determine the cell suppression rate 48hours after GCV was introduced.Results: The RT-PCR and DNA ladder assays confirmed that as a genetic carrier, G 5-PAMAM-D-fol could transfect the recombinant plasmid pcDNA 3-tk into the two prostate cancer cells lines, PC- 3 and LNCaP, and transcribe the HSV-TK gene. MTT assay showed that the two cell lines were significantly inhibited in group A (G5-PAMAM-D-fol/pcD -NA3-tk), and the cell-inhibition rate was higher in group A than in group B (G5-PAMAM-D/pcDNA 3-tk). MTT assay also indi -cated that with an increase of the prodrug concentration, cell growth was not obviously suppressed in group C (G5-PAMAM-D-fol) nor in group D (G 5-PAMAM-D) and the exterminating effect was not significantly greater in group C than in group D. Conclusions: G5-PAMAM-D-fol can efficiently transfect the recombinant plasmid containing the suicide gene into the prostate cancer cells and express the HSV-TK gene in vitro, with a high targeting success and a low cytotoxic-ity to the tumor cells.