The aim of this research was to investigate the phytochemical composition and antimalarial effects of the methanol extract of Erythrina senegalensis leaves (MEES) and its ameliorative effects on some haematological and biochemical alterations in Plasmodium berghei-infected mice. Thirty Swiss mice, 18-22 grams were placed in 6 groups of 5 mice. Group 1 served as normal control. Groups 2-6 were infected with P. berghei. Group 2 was untreated while group 3 was treated with 5 mg/kg body weight of chloroquine. Groups 4-6 were treated orally with 200, 400 and 600 mg/kg b.w. of the MEES for 4 days. The percentage parasitaemia, haematological and biochemical parameters were investigated. Phytochemical analysis indicated the presence of a number of phyto-constituents. The acute toxicity test of the MEES showed no toxicity up to a dose of 5000 mg/kg b. wt. P. berghei infection triggered marked increases in percentage parasitaemia, lipid peroxidation, liver enzymes, kidney function and lipid profile, while the antioxidant and haematological parameters declined in the untreated group. Treatment with the MEES led to significant (p < 0.05) reduction in percentage parasitaemia, lipid peroxidation, liver enzymes, kidney function and lipid profile, and a corresponding increase in antioxidant and haematological parameters, indicating that the MEES reversed complications associated with P. berghei infection.