AIM: To investigate the characteristics and criterion of graft rejection in mice model.METHODS: C57BL/6 or BALB/c mice corneal grafts were grafted onto BALB/c hosts. Each group was divided into two subgroups according to the corneal opacity scores 12d after transplantation. The characteristics of opacity and neovascularization were observed. Mice of the 12^th, 50^th day after transplantation, the grafts biopsy of mice in allogeneic group 1, which opacity score exceed 3, were prepared for histological observation and those restore transparent were endothelial stained.RESULTS: There was no difference of corneal opacity score on the 7^th and 12^th day after operation; the histological results had no disparity between syngeneic group and allogeneic group. On the 12^th day after surgery, the turbidity curve was apparent in grafts with opacity score ＜2. Mononuclear cells were shown in grafts with opacity score reached 3 in allogeneic group 1. Different rejection performance was observed in tissue sections on the 50^th day after surgery.CONCLUSION:Grafts, opacity score exceeds 3 from the 7^th to the 12^th day after operation could not be judged as a rejection. We should pay more attention to the variation of grafts opacity since 12d after corneal transplantation.