This study was conducted to assess the effect of melatonin on the structure of testis and spermatogenesis dynamics in neonate vitrified testis grafts. Neonate vitrified testes, candidates for transplantation heterotopically to experiment or control groups, were warmed in thawing media which had or did not have a supplement of 100 μM melatonin, respectively. Following transplantation, melatonin (20 mg/ /kg/day) or saline solution was intraperitoneally injected into the treated and the non-treated groups, respectively. The initiating spermatogenesis, spermatogonia survival, and structure of tissue in the testis graft were examined. Cell apoptosis (TUNEL assay) and proliferation (Brdu assay) in germ cells were determined. Histological studies revealed the dynamic of the spermatogenesis process in the vitrified testis graft. However, dilation of the lumen accompanied by a disorganised epithelium in the non-treated group was higher than in the treated group. Furthermore, the proportion of apoptotic germ cells together with a reduced proportion of proliferated germ cells was higher in the non-treated group than in the treated group. Overall, the number of seminiferous tubules in the testes grafts of both groups remained steady. However, the non-treated testes grafts contained more damaged seminiferous tubules than the treated ones. The thickness of the seminiferous tubules was greater in the melatonin treated group than in the non-treated group. In fact, the thickness of germinal epithelium was significantly higher in the treated group than in the non-treated group. The study may show a positive effect from melatonin resulting in more grafts restoring puberty. Furthermore, the associated increase in the healthy number of seminiferous tubules suggests that melatonin may have a preventative ischaemia/antioxidant role and in fact may be useful to initiate the spermatogenesis process. (Folia Morphol 2011; 70, 2: 95–102)