Mammalian fertility with aging is thought to decrease due to an increase in aneuploidy, abnormal mitochondrial function, and changes in the expression of oocytes. Although previous studies have reported that naturally aged over 8-month-old female mice have lower fertility, the mechanism of egg quality deterioration is still unknown. In this study, we focus on the effects of aging on ovarian tissue and fertility using young mice (2 months old) and aged mice (8 months old) and clarify the mechanism of age-related deterioration of egg quality. When we examined the fertility by natural mating, the number of pups produced by aged mice was significantly decreased. Histological analysis of ovaries displayed a decrease in the number of remaining follicles, and ovulated oocytes ovulated number by superovulation treatment was also significantly reduced in aged mice. Examination of the fertilization ability in vitro revealed a significant decrease in the fertilization rate in aged mice, whereas there was no difference in gene expression in MII eggs by RNA-seq. These results suggest that the age-related decrease in fertilization ability of mouse oocytes is not due to gene expression in the oocytes themselves, but to inhibition of sperm binding to surface of the zona pellucida.