Celery had been reported as phytochemical antioxidants that contained abundance of flavonoids. Previous studies in diabetic rats and humans reported that reactive oxygen species (ROS) caused further damage to organs, like pancreas, liver. The present study was proposed to discover the benefits of celery on pancreas and liver cell-injury, serum glucose, lipids, and liver enzymes in diabetic rats. Methods: Eighteen diabetic rats with serum glucose more than 200mg/dL were randomly divided into three groups. Group 1, diabetic rats were not given any antioxidants; Groups 2 and 3 diabetic rats were treated with celery orally at 200 mg/kg BW/day and 400 mg/kg BW/day, respectively. After six weeks, the overnight fasting blood was gained from the retro-orbital plexus and centrifuged at 4000 rpm to obtain serum. The animals were sacrificed to harvest the pancreas and liver. The organs were processed in formalin-fixed and paraffin-embedded tissues. Results: Severe pancreas and liver cell damage appeared in Group 1, while moderate and mild damage in Groups 2 and 3. Serum parameters were improved in Groups 2 and 3 compared to Group1. Conclusions: Treatment with celery extract reduced pancreas and liver injury and repaired the serum parameters in diabetic rats.