Abstract: Objective To study the influences of ureaplasma urealitycum (UU) infection on testicular tissue structure and secretion function in rats. Methods Forty clean grade male SD rats were randomly divided into the experiment group A (at 7 d after surgery), experiment group B (at 14 d after surgery), control group C (at 7 d after surgery) and control group D (at 14 d after surgery). There were 10 rats in each group. The experimental groups were injected with 0.6 mL UU4 through bladder. In the same way, the control groups were injected with the same volume of UU liquid medium. At day 7 and 14 after injection, the structures of testis of all rats were observed by light microscopy and spermatogenic cells by transmission electron microscopy. The content of testosterone in plasma and testicular fluid were detected by chemiluminescence method. Results The changes of inflammatory pathology (including the layer and amount of spermatogenic cell decreasing, inflammatory cell infiltrating and mature sperms decreasing) in the testis of group A and group B were found by light microscopy, and the inflammatory changes in group B were lighter than those in group A. The structures of testicular tissue in group C and group D were normal. The apoptosis performances of germ cell (including the cell membrane corrugated, nuclear chromatin concentration and nuclear rupture) in the testis of group A and group B were found by transmission electron microscopy, and the changes in group B were lighter than those in group A. The structures of germ cell in group C and group D were normal. The levels of plasma testosterone in group A and group B were significantly lower than that in group C and group D (P<0.01), the difference between group A and group B was not statistically significant. The testosterone level in testis interstitial fluid in group A was significantly lower than that in other groups (P<0.01), the differences between other groups were not statistical significant. Conclusion The testicular tissue of UU infected rats can have various pathological damage and functional changes, further confirming that UU infection can cause male infertility. The pathological damage and functional changes of the testicular tissue of rats after UU infection can be gradually restored with the extension of the duration of the disease.