The acute toxicity of promethazine hydrochloride (phenergan) to Clarias gariepinus fingerlings was conducted using static bioassay under laboratory conditions. The 96h LC50 was determined as 172.5 mg/1. Mean mortality was 5, 10, 20, 50, 100% in the concentration of 69, 103.5, 138.0, 172.5 and 207 mg/1 respectively, while there was no mortality in the control treatment. There were significant differences (P<0.05) on the effect of concentration, the higher the mortality of C. gariepinus fingerlings while toxicity of phenergan increased with duration of exposure. C. gariepinus showed increased hyperactivities, cell deformation, lesions and necrosis during the period of exposure. The physicochemical parameters also showed a slight increase as the concentration increased
