In this work, we investigate changes in the secretory function of Sertoli cells in diabetic rats and its correlation with testicular damage. Diabetes was induced by intraperitoneal injection of streptozotocin (55 mg/kg/i.p.) in adult rats. Eight weeks later, testicular tissue was harvested. Serum inhibin B (INHB) and testosterone (T) levels were measured by ELISA. The levels of secretory proteins, such as androgen-binding protein (ABP) and transferrin (TF), were measured by western blot analysis. Testicular damage was evaluated by hematoxylin and eosin staining, and apoptosis was identified by terminal-deoxynucleotidyl-transferase-mediated dUTP nick end labeling (TUNEL). Seminiferous tubular sperm formation was evaluated by the Johnsen's score. In diabetic rats, ABP protein levels (P = 0.038), serum INHB (P = 0.031), and T levels (P = 0.039) decreased greatly, whereas the decrease in TF protein levels (P = 0.247) was not significant. Additionally, TUNEL-positive cells (P = 0.000) increased and the Johnsen's score (P = 0.000) decreased in diabetic testes. These results suggest that the secretory function of Sertoli cells in diabetic rats was damaged. The altered secretory function of Sertoli cells may be responsible for disturbed spermatogenesis.