To investigate the expression of FasL in rat cryptorchidism and its significance.Twenty-four male SD rats (22-day old) were randomly divided into two groups: unilateral cryptorchid group (n = 12) and pseudo-operation group (n = 12). When the rats were 110-day old, blood samples were taken and the rats were killed for analysis. Immunohistochemical method (SP) was used to detect FasL expression in testes and ELISA method to detect serum antisperm antibody (AsAb).The positive FasL expression rates in cryptorchid and contralateral testes were significantly higher than those in pseudo-operation group (P < 0.001). The serum AsAb positive rates in the cryptorchid group and the pseudo-operation group were 41.7% and 0, respectively, with significant difference(P < 0.01).FasL expression upregulating in both testes of the unilateral cryptorchid rat may be a protective response of the testis to autoimmunity.