Diabetes mellitus (DM) is a chronic metabolic disorder characterized by persistent hyperglycemia that may impair testicular function, including spermatogenesis and steroidogenesis. Creatine, an endogenously synthesized nitrogenous compound and one of the main reservoirs in the testes, is widely used, particularly among men. However, evidence regarding its effects on male reproductive health, especially under DM, remains limited. This study evaluated the impact of creatine supplementation on testicular morphology in streptozotocin-induced diabetic rats. Forty-eight adult Wistar rats were randomly assigned to four groups (n = 12 each): C, control; CT, creatine; D, diabetes; and DT, diabetes + creatine. Creatine-enriched chow was administered in two phases: a loading phase (13%; 130 g/kg) for 5 days prior to DM induction, followed by a maintenance phase (2%; 20 g/kg) for 35 days. Biochemical, histomorphometric, histopathological, and immunohistochemical analyses were performed. Compared to controls, group D showed increased seminiferous tubule and epithelial proportions, epithelial height, tubular volume (TV), and tubulosomatic index (TSI), while intertubular proportions decreased. DT normalized most morphological parameters to C group levels, and attenuated the diabetes-induced increases in TV and TSI. In the intertubular compartment, group D showed increased Leydig cell and connective tissue proportions versus C, while DT exhibited larger lymphatic spaces (vs. D) and the greatest Leydig cell nuclear diameter among all groups. Histopathological degeneration was significant in both D and DT and remained higher than in control levels. Immunohistochemistry revealed reduced SOD1 and increased NFκB-p65 expression in DT compared to D. These findings indicate that creatine supplementation is associated with morphometric and histopathological changes in the testicular parenchyma of diabetic rats, along with alterations in oxidative stress and inflammatory markers. Further studies are required to determine the functional implications for male reproductive health.