The in vitro antibacterial activity of crude methanolic extract of the seeds of Garcinia kola was investigated. The extracts exhibited antibacterial activities with zones of inhibition ranging from 10 mm to 25 mm. The minimum inhibitory concentration of the diethyl ether fraction was between 0.313 and 5.0 mg/ml, while that of butanol fraction varied from 0.157 to 5.0 mg/ml. The butanol fraction killed about 77% of Bacillus anthracis and 79% of Escherichia coli cells within 120 min at a concentration of 5.0 mg/ml. Protein leakage from the B. anthracis and E. coli cells when exposed to the butanol and diethyl ether fractions was observed. We conclude that Garcinia kola seed extract has a broad spectrum antibacterial activity, with the butanol and diethyl ether fractions being bactericidal as exemplified by the killing rate and protein leakage regimes, which suggest cell membrane disruption as a mechanism of action of the extract.