This study investigated the effect of the methanol leaf extract of Annona muricata (MEAM) in the serum chemistry of albino rats experimentally infected with Trypanosoma brucei brucei. A total of 20 adult male albino rats weighing between 78g and 100g were used for the study. They were randomly assigned into 4 groups (I shyshyshyshyshyshyshyshyshyshyshyshyshyshyndash IV) of five rats each. Groups I and II were infected intraperitoneally with 1.0 times106 trypanosomes suspended in 0.2ml of Phosphate Buffered Saline (PBS) on day 8 of experiment. Group I was treated was treated with 200 mg/kg of MEAM orally every day for 3 days following detectable parasitaemia (4-5days of post infection). Group II was treated with 7.0 mg/kg of diminazene aceturate intramuscularly on day 14 of experiment (6 days post infection). Group III served as the uninfected untreated control while Group IV was uninfected and treated with 200mg/kg MEAM. Parameters such as Parasitaemia, Packed cell volume (PCV), Haemoglobin concentration, Total leucocytes count, Differential leucocytes count,Rectal temperature and serum activities of Aspartate aminotransferase (AST),Alanine aminotransferase (ALT) as well as serum levels of creatinine, Urea, Albumin,Total protein and Globulin were used to assess the anti trypanosomal activity of MEAM. The acute toxicity test and the in vitro anti nbsptrypanosomal activity of the extract were studied using standard methods prior to commencement of the study. The results of the acute toxicity test showed the LD 50 of the MEAM to be 447 mg/kg whereas the LC50 of the extract was recorded at 0.01 in vitro. The pre- patent period of infection was 3days. Treatment with diminazene aceturate cleared the Parasitaemia in group II. An overall significant decrease (Plt 0.05) in PCV and Haemoglobin were observed in the infected groups. Similarly, a significant decrease (Plt 0.05) in total leucocytes count was also seen in the infected groups. This decrease was mainly due to a significant decrease (Plt0.05) in the leucocytes count of the infected groups. There was a significantly higher (Plt0.05) mean serum AST and ALT activities in rats of group I than those of group II, III and IV. A significantly higher (Plt0.05) mean serum creatinine level was also seen in groups I and IV than in groups II and III, whereas the mean urea level was significantly higher (Plt0.05) in group I than in groups II, III and IV.It is therefore concluded that MEAM showed an in vitro anti trypanosomal activity. However, this was observed in vivoat the dose and route of administration., MEAM may be nephrotoxic as seen with the elevated levels of creatinine in group IV.