Psychotria microphylla is an ichthyotoxic botanical used to stupefy fish prior to harvesting in aquatic systems. The current study investigated the effect of P. microphylla leaf extract on the oxidative stress and biochemical parameters of the giant African land snail, Achatina achatina. Adult A. achatina were administered 0.35, 0.45 and 0.55 mg l^–1 leaf extract of P. microphylla and sampling was done after 24, 48, 72 and 96 h durations. Oxidative stress was evident by the significant increase in lipid peroxidation (LPO). Maximum LPO values of 36.13% and 63.69% were observed in A. achatina administered 0.55 mg l^–1 of the leaf extract at 24 h and 96 h respectively. Superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) significantly decreased, whereas the values of glutathione reductase (GR) increased significantly compared to the control. Extract-induced toxicity was evident by the significant increase in alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activity relative to the control. The current findings indicate the potential toxicity of P. microphylla and suggest that it could be used for control of terrestrial snail pests.