【Abstract】Objective To observe the effect of microRNA (miR) -204-5p on apoptosis of ovarian granulosa cells in rats with premature ovarian failure (POF), and explore the regulatory mechanism. Methods BMSCs were isolated from rats in vitro. The recombinant lentivirus vector containing antisense oligonucleotide sequence of mir-204-5p gene was transferred into BMSCs to obtain BMSCs stably transfected with LV-rno-ASO-miR-204-5p. Seventy-five Wister rats were divided into control group, POF group, BMSCs group, shRNA group, shRNA-BMSCs group, 15 rats in each group. The shRNA group, BMSCs group and shRNA BMSCs group were injected with lentivirus vector. BMSCs cells and BMSCs cells stably transfected with lentivirus vector. The control group and POF group were injected with normal saline. The recovery of estrus cycle in each group was observed. The serum levels of FSH and E2 were compared before and 28 days after intervention in each group. Ovarian morphology and apoptosis rate of granulosa cells were observed. Mir-204-5p mRNA and mitogen activated protein kinase (MAPK), B-cell lymphoma-2 gene (Bcl-2), Bcl-2 related X protein (Bax), cysteine protease-3 (Caspase-3) mRNA and protein expressions in ovarian tissue were detected. Results After intervention, the estrous cycle in the POF group did not recover. The estrous cycle in the three intervention groups all recovered. The recovery rate of the estrous cycle in the shRNA-BMSCs group was higher than that in the BMSCs group and shRNA group (P＜0.05). Pathological staining showed that the number of primordial follicles, primary follicles, secondary follicles and sinus follicles in the BMSCs group, shRNA group and shRNA-BMSCs group were all higher than those in the POF group, but still less than the control group (P＜0.05). The number of follicles at all levels in the shRNA-BMSCs group were more than those in the BMSCs group and shRNA group (P＜0.05). After intervention, the serum FSH level, apoptosis rate of ovarian granulosa cells, the mRNA relative expression of miR-204-5p and the mRNA and protein relative expressions of MAPK, Bax, Caspase-3 in ovarian tissue of BMSCs group, shRNA group and shRNA-BMSCs group were lower than those of POF group, and shRNA-BMSCs group were lower than those of BMSCs group and shRNA group, while which were still higher than those of control group P＜0.05). The level of serum E2 and the relative expressions of Bcl-2 mRNA and protein in ovarian tissue were higher in BMSCs group, shRNA group and shRNA BMSCs group than in POF group, and higher in shRNA-BMSCs group than in BMSCs group and shRNA group, while which were lower than still than in the control group (P＜0.05). Compared with BMSCs group, shRNA group showed lower expression of mir-204-5p mRNA in ovarian tissue (P＜0.05). There was no significant difference in number of follicles at all levels, serum FSH, E2 level, apoptosis rate of ovarian granulosa cells and relative expression of MAPK, Bcl-2, Bax, Caspase-3 mRNA and protein in ovarian tissue (P＞0.05). Conclusion Down-regulation of miR-204-5p expression can enhance the improvement of BMSCs on ovarian structure and function of POF rats and inhibit the apoptosis of ovarian granulosa cells, which may be related to the down-regulation of MAPK, Bcl-2, Bax, Caspase-3 gene and protein expression.