Background: Autism spectrum disorder (ASD) is identified by developmental deficits that lead to repetitive/stereotypic patterns of behavior and impaired social interactions. Studies have been indicated that exercise can decrease stereotypic behaviors in animal models of ASD. This research was designed to discover the effects of different models of forced exercise on stereotypical behaviors in a rat model of ASD induced by thimerosal (THIM). Materials and Methods: Fifty-six male Wistar rats were divided into eight groups. The rats were received saline (1 ml/kg) or THIM (300 μg Hg/kg) by four intramuscular injections on 7, 9, 11, and 15 postnatal days. The rats were also treated by several protocols of treadmill exercise, including non-sedentary, sedentary, protocol 1, protocol 2, and a combination of protocols 1 and 2. Results: Our study showed that THIM decreased the grooming time compared to the control group. Moreover, protocol 2 exercise significantly decreased grooming time in stranger zone 2 compared to the THIM group. Conclusions: Our results showed that stereotypical behaviors exaggerated by THIM and moderate exercise could improve ASD-associated behaviors in the THIM-treated rats. Hence, moderate exercise may be a useful protocol for the treatment of ASD. [GMJ.2022;11:e1990]