Celecoxib is intended for acute pain, menstrual cramps, pain, and inflammation of osteoarthritis and rheumatoid arthritis. The aim of this study was to evaluate the effects of celecoxib (10 and 50 mg/kg/day) treatment on rats orally for 28 days. We examined effects on some biochemical parameters and kidney and liver tissues of celecoxib-treated Wistar albino male rats. At the end of the study, hepatic and renal function tests were performed and liver and kidney of rats were microscopically examined to detect systemic toxicity of celecoxib. Celecoxib-treated rats had statistically significant decreases of cholesterol, total bilirubin, total protein, urea, globulin, blood urea nitrogen, phosphorus, and calcium. Serum gamma glutamyl transferase levels increased in 10- and 50-mg/kg/day celecoxib-treated rats. Histological examinations showed mononuclear cell infiltration, hyperplasia, and cellular degeneration in liver and tubular damage and mononuclear cell infiltration in kidney. We suggest that high doses of celecoxib may cause changes in liver and kidney histopathology, liver function, and in some biochemical parameters.