Objective To investigate the development of neonatal mouse testis in castrated immunodeficient mice by monitoring the graft survival and weight and observing the structure of seminiferous epithelium and the composition of spermatogenic cells in grafts. Methods Neonatal Kun ming mouse testis were grafted under the skin of castrated nude mice (7-12week-old). Grafts were then taken out at different time intervals (namely 16 time points: 3 days, 1-11 weeks respectively and 3-6 months respectively). The survival rate of grafts was calculated and the wet weight was measured. Histological analysis was performed for the observation of the structure of seminiferous epithelium and the composition of spermatogenic cells in grafts. Results Four hundrcd and five grafts recovered out of 450 testis grafted, resulting in a recovery rate of 90.0%. The graft weight increased more than 40 times. The developmental pattern of seminiferous tubules and the appearance time of various spermatogenic cells in grafts were similar as seen in intact mice. Eight weeks after the grafrting, an increasing degradation of seminiferous epithelium was observed.Conclusion When neonatal mouse testis were grafted into nude mice, the developmental course was similar as that in normal donors. The optimal retrieval time of round spermatids and sperms was around the end of the first spermatogenesis wave, about 5-7weeks after the grafting procedure.