Objective:To construct an adenovirus-mediated mouse endostatin vector (Ad-mEndo) and to observe its inhibitory effect on the pulmonary metastasis of osteosarcoma in nude mice, so as to discuss the relationship between ES expression and the pulmonary metastasis of osteosarcoma. Methods: Recombinant adenovirus plasmid pDC315-mEndo was constructed and used to prepare recombinant Ad-mEndo. Osteosarcoma MG-63 cells were subcutaneously injected into the right fore limbs to establish nude mouse model of osteosarcoma; and the models were randomly divided into 3 groups: Ad-mEndo group, Ad-EGFP group and PBS group; animals receiving no transplantation served as blank control. The corresponding agents were injected (20 ?l per time) for a consecutive of 5 times on a weekly basis. The tumor volumes, histopathological characteristics were observed; ELISA was employed to examine the serum ES level. Animals were sacrificed 7 weeks later and the pulmonary metastasis was observed. Results: Sixteen days later,the tumor volume was (1.53?0.05)cm3 in Ad-EGFP group, (1.56?0.07)cm3 in the PBS group, and (0.91?0.03)cm3 in the Ad-mEndo group, with the tumor inhibitory rate being 40.7% in the last group. The serum ES level in the Ad-mEndo group was significantly higher than that of the other groups (P