Abstract： Objective To study the inducement of U251 glioblastoma cell apoptosis in vivo through up-regulating PUMA expresion and knocking down miR-221/222, and explore its mechanism.Methods Nude mouse xenograft models were established in 5-week-old BALB/c nude mice by subcutaneous vaccination of U251 glioblastomas; 1 week later, they were treated with intratumoral injection of lipofcctamine-mediated miRNA-221/222 antisense oligonucleotides (GroupA), nonsense sequences (Group B) and controls (Group C),respectively (n=8).The tumor growth was monitored until the end of observation period (28 d after the treatment) and pathological changes of the glioblastoma tissues were observed by HE staining at the end of observation.Fluorescence in situ hybridization (FISH) and real-time PCR were employed to measure the miR-221 and miR-222 expressions. Terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling (TUNEL) assay was used to detect the apoptosis of glioblastomas.Immunohistochemistry and Westem blotting were used to detect the expressions of PUMA,bax,bcl-2 and p53 in removed tumor specimens. Results The volume in Group A was significantly smaller than that of those in group B and group C 6-28 dater treatment (P=0.006). The miR-221 and miR-222 mRNA expressions in Group A were significantly decreased as compared with those of those in group B and group C.HE staining indicated that decreased heteromorphism and reduced number of new vessels in Group A were noted as compared with those in group B and group C.The cell apoptotic index in Group A was significantly higher than that in group B and group C (P＜0.05).Immunohistochemistry showed that the expression levels of PUMA and bax in Group A was significantly up-regulated as compared with those in group B and group C, while the expression of bcl-2 in Group A was significantly down-regulated as compared with that in group B and group C; and no significant changes were noted in the p53 expression. Conclusion By up-regulating PUMA expresion,knocking down miR-221/222 can induce U251 glioma apoptosis in vivo.