Background: Garcinia kola seed is consumed indiscriminately in Nigeria without recourse to its potential toxicity. Therefore, this study was aimed at assessing the toxicity of the aqueous extract of G. kola seeds on selected tissues of male rats. Methods: Thirty male rats (215.00 ± 18.58 g) were assigned into four groups: A, B, C and D which received 0.5 ml of distilled water, 25, 50 and 100 mg/kg body weight of the extract respectively, once daily for 7 days. Biochemical indices of organ damage and toxicity were determined using standard methods. Results: The extract significantly (P<0.05) increased the testes-body weight ratio, activities of testicular alkaline phosphatase (ALP), heart, testes and serum gamma glutamyl transferase (GGT) activity, serum concentrations of uric acid, K+, creatinine and PO43-. The liver-body weight ratio, activities of kidney and serum ALP, liver, heart and serum alanine and aspartate aminotransferases (ALT and AST), serum and testicular acid phosphatase (ACP), concentrations of serum albumin, globulin, urea, Na+ , HCO3-, conjugated and total bilirubin were reduced. The heart- and kidney-body weight ratios and liver ALP were not significantly (P>0.05) altered. Conclusion: The treatment related alterations in the present study indicates that the aqueous extract of G. kola seeds at the doses of 25, 50 and 100 mg/kg body weight caused functional toxicity to the organs of the animals and thus not safe as an oral remedy.