BACKGROUND AND OBJECTIVE: Busulfan is one of the cancer treatment drugs that cause infertility of the patient. In traditional medicine, one of the important properties of cinnamon is enhancement of fertility. The aim of this study was to investigate the effect of cinnamon on the physiological structure of testes and fertility rate of busulfan-treated rats. METHODS: In this experimental study, 24 adult male rats were divided into 3 groups of 8 subjects, Sham: healthy rats without intervention. Control group: Busulfan-sterilized rats (15 mg/kg) intraperitoneal injection, Cinnamon group: Busulfan-treated rats + cinnamon extract (200 mg/kg) for fourteen days. The testicles length, width and weight parameters as well as the formation of germinal cells were analyzed by H & E staining and optical microscopy. FINDINGS: The number of spermatogonia cells, primary spermatocytes and spermatid in the cinnamon group was 72.25±12.63, 61.71±11.47, and 79.1±10.02, and in the control group was 51.83±23.37, 31.67±5.27 and 38.67±15.7 respectively, and the increase in cinnamon group was significant (p<0.005). The testicles length, width and weight parameters in the cinnamon group were increased compared to the control group (busulfan). The thickness of germinal epithelium in the cinnamon and control group was 53.46 ± 16.44 and 30.4±10.21 respectively, which was significantly higher in the cinnamon group (p<0.001). CONCLUSION: According to the findings of this study, cinnamon extract has positive therapeutic and protective effects on testicular tissue and increases sperm production in busulfan-treated rats