Abstract: Some toxic effects of the aqeous leaf extract of Anogeissus leiocarpus was evaluated in rats using changes in haematological and biochemical parameters as well as body weight changes. The results indicate that the extract had no significant effect (p>0.05) on haematological parameters except the packed cell volume and lymphocytes. Significant (p<0.05) dose-dependent increase were observed in serum levels of aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase. Serum sodium and potassium were not affected by extract administration. However, total protein, bilirubin, urea and cholesterol as well as body weight values were significantly lower than in the control especially in groups that received higher doses. The results of this study therefore suggest that the leaf extract of this plant could affect feed intake and utilization and also elicit some changes in biochemical parameters of rats.