This is a retrospective, observational study to evaluate the effect of maternal age on the outcomes of in vitro fertilization and embryo transfer (IVF-ET). 11830 IVF-ET cycles from 10268 women were included. Four groups of different maternal age periods were compared. The groups were 21-30 years old group (4549 cycles), 31-35 years old group (4424 cycles), 36-40 years old group (2429 cycles), and over 40 years old group (428 cycles). The mean starting dose of Gn and mean total dose of Gn in each cycle were significantly higher (P<0.01), while the mean retrieved oocyte number was significantly lower (P<0.01) in groups of higher maternal age period than those in each of the lower groups. The biochemical pregnancy rate and the clinical pregnancy rate were significantly lower (P<0.01), while the miscarriage rate was significantly higher (P<0.01) in groups of higher maternal age period than those in the lower groups. No difference was found in two-pronuclear zygotes (2PN) rate and good quality embryo rate among different groups. Birth defect rate was also comparable in the born babies in different groups. In the group with patients' age over 40 years old, the pregnancy rate was 26.87%, the clinical pregnancy rate was 19.39%, while the miscarriage rate after clinical pregnancy was 36.14%. To draw the conclusion, patients with higher maternal age had worse IVF outcomes. In women of fertile age, patients between 20 and 30 years old have the best IVF outcomes. Patients over 40 years old have poor IVF outcome and high miscarriage rate, which suggested the necessity of preimplantation genetic screening (PGS).