Abstract Objective: Thymol, a natural aromatic monoterpene phenol derived from thymus, possesses anti-inflammatory benefits. Here, we evaluated the potential of thymol therapy in improving an animal model of ulcerative colitis. Materials and methods: Luminal instillation of acetic acid was used to induce colitis in male Wistar rats. Treatment groups daily received prednisolone (2 mg/kg, orally) or thymol (100 mg/kg, orally) for 10 consecutive days. Then, the rats were euthanized and tissue specimens were collected for evaluation of cyclooxygenase-2 (COX-2) expression by immunohistochemistry. Furthermore, the levels of total protein, nitric oxide, myeloperoxidase, malondialdehyde, IL-1, IL-6, and TNF-α were monitored in colonic homogenates. Eventually, the relative...