The study was designed to investigate the analgesic effect of the aqueous leaf extract of Fagara tessmannii engl using the acetic acid-induced pain model in Wistar rats. Twenty rats were divided into five groups of four rats each. Group 1 received distilled water while groups 2-5 received 0.2 ml/kg BW of 0.6% intraperitoneal injection of acetic acid 30 mins after treatment with extracts and reference drug and writhing counted. Rats were sacrificed and blood was collected for biochemical and heamatological analyses. Also, Gas chromatography and phytochemical characterization of alkaloids in the aqueous leaf extract were done. The result revealed a significant decrease (p≤0.05) in the mean number of writhing in group 4 and non-significant decrease (p≥0.05) in groups 3 and 5 when compared to control group. Percentage inhibition of nociception in groups 3, 4, and 5 were 2%, 41.7%, and 10.5%, respectively. Non-significant differences (p≥0.05) in WBC, lymphocyte, neutrophil, eosinophil, and basophil counts in groups 5, 4, and 3 were observed when compared to normal and negative control groups. Monocyte count and ESR significantly decreased (p≤0.05) when negative was compared to normal control. CRP, IL-6, and PTG-S1 concentrations significantly increased (p≤0.05) when the negative control group was compared to the normal control. Groups 5 and 4 for CRP and 3 and 4 for IL-6 concentrations were significantly reduced (p≤0.05) while PTG-S1 was none significantly reduced in a dose-dependent manner when compared to the negative control. Some abundant alkaloids identified were acetic acid (12.3442%), benzoic acid (11.7984%), phenol, 4-methoxy-, acetate (6.8281), and phenol (4.3901%). Aqueous leaf extract of Fagara tessmannii Engl exhibited antinociceptive potential through the action of bioactive constituents.