〔Abstract〕 Objective To investigate whether the application of melatonin(MT) in embryo culturein vitrocan improve the treatment effect ofin vitrofertilization embryo transfer(IVF-ET) in patients with decreasing ovarian reserve(DOR). Methods 128 DOR patients receiving assisted reproductive therapy were collected. All patients were treated with an antagonist scheme of super-ovulation. Patients were divided into melatonin group(n=56) and control group(n=72) according to whether melatonin(melatonin concentration 10-9mol/L) was added into embryo culture medium. Results There was no statistically significant difference in oocytes fertilization rate and cleavage rate between the two groups during later embryo culture, but blastocyst formation rate(65.22%vs56.16%) and high-quality blastocyst rate(52.96%vs40.94%) in the melatonin group were higher than those in the control group, and the differences were statistically significant(P<0.05). There were no significant differences in the implantation rate(50.00%vs38.67%) and clinical pregnancy rate(48.39%vs46.00%) of blastocysts after freezing-thawing between the two groups, but the cycle number of high-quality blastocysts obtained in the melatonin group was higher than that in the control group(85.71%vs69.44%), and the difference was statistically significant(P<0.05). Conclusion In a way, the application of melatonin in thein vitroculture of early embryos can promote the development of oocytes in patients with DOR, improve the quality of embryos, and finally substantially improve the therapeutic effect of such patients.