Aim: This study aimed to evaluate the antioxidant potentials of Pentaclethra macrophylla seed (Ugba) on mercury-induced hepatic, renal and testicular oxidative stress in male Albino Rats.
 Study Design: This study is an experimental study.
 Place and Duration of Study: Department of Animal and Environmental Biology Animal House, Rivers State University, Port Harcourt, Nigeria, between January 2019 and January 2021.
 Methodology: Thirty-six (36) adult male albino rats weighing approximately 135±1.5g were purchased from the University of Port Harcourt, Rivers State, Nigeria. They were housed in plastic suspended cages, placed in well-ventilated conditions and provided with rat diet and water, and acclimatized for two weeks. Fresh matured seeds of Pentaclethra macrophylla (African oil bean seed) were sourced locally from markets in Imo state, Nigeria. The maceration technique was used to carry out an ethanolic extract of the plant seed. Mercury chloride salt was purchased from Port Harcourt. A standard dose of 3.0mg/kg body weight of mercury chloride obtained from acute toxicity study dose determination was administered to the rats for 30 days after they were divided into six groups of six rats per group. After 30 days, all the animals were weighed, anesthetized using chloroform. Tissue samples of liver, kidney, and testis were collected and homogenized in phosphate-buffered saline and stored at 40C for determination of oxidative stress assessment. Malondialdehyde, Reduced Glutathione (GSH), Catalase Activity, superoxide dismutase (SOD) activity, Glutathione Peroxidase Activity were analyzed using the homogenized sample. Data were expressed as mean ±SD, and the statistical analysis was performed with the SPSS statistics 23.0, and p values less than .05 were considered statistically significant.
 Results: The results showed that there were significant increases (P<.05) in the liver, kidney, and testicular MDA and significant decreases (p<.05) in SOD, CAT, GSH, and GPx activities in group 2 rats versus control. However, after treatment with different concentrations of Pentaclethra macrophylla, MDA activity significantly decreased (P<.05), while SOD, CAT, GPx, and GSH significantly increased (P<.05).
 Conclusion: The results obtained from the study showed that mercury chloride has the potential to cause liver, kidney, and testicular toxicity to adult male albino rats, and this toxicity was exerted majorly through oxidative stress and lipid peroxidation. However, treatment with Pentaclethra macrophylla seed extract ameliorated oxidative stress.