Background and Aim: Diabetes is a well-known disease with such complications, as retinopathy, nephropathy, and gastropathy. This study aimed to investigate the effects of thiamine and lead acetate on the colon of induced-alloxan diabetic rats; the effects of which become obvious in the treatment or reduction of tissue complications caused by diabetes. Methods & Materials: In this study, 63 rats weighing 200 g were divided into 9 groups, as follows: 1) Group of diabetes+pb acetate 200 ppm; 2) Group of thiamin+pb acetate 200 ppm; 3) Group of thiamine+pb acetate 1000 ppm; 4) Group of diabetes+thiamine+Pb acetate 1000 ppm; 5) Diabetes group; 6) Group of diabetes+thiamine; 7) Group of diabetes+thiamine+acetate 200 ppm; 8) Group of diabetes+pb acetate 1000 ppm, and 9) the control group. After 20 days, the study samples were removed from the abdominal cavity and the slides were prepared by routine tissue method. Then, the slides were evaluated for stereological and histomorphometric studies. Ethical Considerations: This study was approved by the Faculty of Veterinary Medicine, Shahrekord University (Code: GRN1M1903). Moreover, all methods used in the present study, including facilitation, were conducted per the ethical principles of animal restraint. Results: The mean thickness of mucosa-sub-mucosa suggested significant differences in groups 6 and 7, compared to other treatment groups. There was a significant difference in the thickness of the muscle layer between the control and all treatment groups except for groups 2, 6, and 7. There was no significant difference in the mean thickness of advantia layer in groups 1, 7, and 8, and the control group. The obtained results also indicated a significant difference concerning different layers of colon tissue between group 1 and controls. Conclusion: Based on the present research results, thiamine presented enhancing effects on muscle layer thickness and adventitia layer thickness. Furthermore, the area of the mucosal layer was not affected by the improving effects of thiamine.