This study aimed to investigate the protective effect of boric acid (BA) supplementation against oxidative stress (OS) in ovariectomized rats. A total of 48 nonpregnant female Wistar albino rats (180-250 g) were used in the experiment. The rats were divided into six equal groups (n = 8): Control, OVX, OVX + 5 mg/kg BA (OVX + BA5), OVX + 10 mg/kg BA (OVX + BA10), 5 mg/kg BA (BA5), and 10 mg/kg BA (BA10). The rats were intraperitoneally anesthetized with a combination of ketamine hydrochloride (85 mg/kg) and xylazine (10 mg/kg) and underwent a bilateral ovariectomy. Supplementation with 5 mg/kg and 10 mg/kg BA via oral gavage was started 2 weeks after ovariectomy and continued for 20 days. Catalase (CAT), glutathione S-transferase (GST), glutathione peroxidase (GPx), glutathione (GSH), and malondialdehyde (MDA) levels in the liver, kidney, and brain tissues of rats were analyzed by the spectrophotometric method. MDA concentrations in the liver tissue was increased in the OVX rats compared to the control group (p <0.05). Liver GST activity was significantly decreased in the OVX rats, but it was increased with 5 mg/kg and 10 mg/kg BA supplementation (p <0.05). Mean kidney GSH, GPx, and CAT activities in the OVX rats were increased with 5 mg/kg and 10 mg/kg BA supplementation (p <0.05). In the brain tissue, GST activity was increased in the OVX rats treated with 10 mg/kg BA (p <0.05). These results indicate that BA supplementation can enhance antioxidant defense mechanisms against OS after ovariectomy in female rats.