Abstract: Guava leaves have been used to treat cough and pulmonary diseases; they have also served as anti inflammatory and haemostatic agent in china. This work is therefore aimed at investigating the effects of guava leaf extract on the liver enzymes of adult wistar rats. Twenty apparently healthy wistar rats were used for this study. They were allocated into four groups (A, B, C & D) of five animals each. Group A served as the control and was orally administered with 0.5ml of distilled water; the experimental groups B, C, & D were orally administered 250mg/kg, 500mg/kg and 750mg/kg of guava leaf extract respectively for fourteen days. Twenty four hours after the last administration, the animals were dissected. Blood for serum preparation were collected through cardiac puncture. The activities of serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphotase (ALP) were determined using randox kit method. There were no biochemical alterations in the activities of serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphotase (ALP).