Objective To study the effect of recombinant adenovirus mediated p53 gene on reversing multidrug resistance and expression of P-gp in MCF-7/ADR human breast cancer xenografts. Methods MCF-7/ADR human breast cancer cells were injected into nude mice. The experimental mice with xenografts were randomized into groups of control, rAd-p53, adriamycin, rAd-p53+adriamycin. The growth of tumor was observed. Expression of P-gp in several groups was assessed by Western blotting. Results The inhibitory rate after administration of rAd-p53, adriamycin, and rAd-p53+adriamycin were 42.05%,49.21%, and 69.97%, respectively. There was significant difference between all treatment groups and control group (P＜0.05). And inhibition in group rAd-p53+adriamycin was more significant than inhibition in group rAd-p53 and group adriamycin. The expression of P-gp in groups of control, rAd-p53, adriamycin, rAd-p53+adriamycin were (0.5964±0.0806), (0.5506±0.0127), (0.5641±0.0055), and (0.4652±0.0982), respectively it was decreased significantly in group rAd-p53+Adriamycin. Conclusions rAd-p53 can effectively reverse the multidrug resistance of MCF-7/ADR xenografts in nude mice. And it can inhibit the expression of P-gp.