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Objective To investigate effects of aging on spermatogenesis in testis, sperm maturation in epididymis, and fertility in mice.Methods Testicular specimens, caput epididymal sperm and cauda epididymal sperm were obtained from Kuming mice (18-month aged group, n=15; 6-month young group as control, n=15). The testicular histological examinations and quantitative evaluations on spermatogenesis were performed. Sperm parameters including sperm density, sperm viability, sperm motility, and normal morphological rate were assessed. The fertilization rate and embryo development were measured by in vitro fertilization and embryo culture.Results The histological changes of testes in aged mice were mainly seminiferous tubule atrophy and hypospermatogenesis. In aged testes, a significant decline was found in the numbers of round spermatids and elongated spermatids per Sertoli cell (P＜0.01). Sperm density, sperm motility and normal morphological rate in caput epididymis and cauda epididymis in aged mice significantly decreased (P＜0. 05). The fertilization rate and embryo development of aged group were lower than those in the control(P＜ 0.01).Conclusions Spermatogenesis and sperm functions could be maintained in the aging male. However, aging affects spermatogenesis and sperm maturation, which leads to lower the quality of sperm, including sperm fertilizing capacity. The development of embryo from aging sperm would have more abnormalities.