Abstract: Objective To study the effects of bone marrow mesenchymal stem cells(MSCs)transplantation on the expressions of β-catenin and c-myc mRNA of thymoma induced by ionizing radiation in mice and to provide theoretical basis for exploring the effect of MSCs in tumor genesis and development. Methods MSCs from C57BL/6 mice were cultured through whole bone marrow adherence in vitro.The model of thymoma was induced by whole-body X-irradiation. The mice were divided into three groups:the normal,irradiation and treatment group with MSCs after irradiation.The expressions of β-catenin and c-myc mRNA were detected by reverse transcription-PCR(RT-PCR)6 months after the irradiation. Results The expression of β-catenin mRNA in the irradiation group was significantly higher than that of in the nomal control(P<0.05),and the expression in the irradiation+MSCs group was lower than that in the irradiation group.The expression of c-myc mRNA in the irradiation group was higher than that of in the nomal control,and the expression in the irradiation+MSCs group was significantly lower than that in the irradiation group(P<0.05). Conclusion MSCs could inhibit tumor proliferation through inhibiting the abnormal expressions ofβ-catenin and c-myc mRNA.