Leaf ethanolic extracts of six Senna species namely S. occidentalis, S. hirsuta, S. siamea, S. obtusifolia, S. polyphylla and S. alata were obtained using the cold extraction method. The extracts were tested for antimicrobial activity against five organisms, namely Escherichia coli, Klebssiella pneumonia, Staphylococcus aureus, Streptococcus pneumonia and Salmonella typhi. The agar well diffusion method was used to carry out this test. The study on antimicrobial activities shows that ethanolic extracts of the six Senna species possess antibacterial activity against human pathogens used in this study. The antibacterial activities of the extracts were more pronounced at higher concentration than at lower concentration in the species of Senna investigated. However, Senna alata showed more antimicrobial acivity. The minimum inhibitory concentration (MIC) of the plant extracts ranged from 21.5 mg/ml to 62.5 mg/ ml with Senna alata having the lowest value (31.25 mg/ ml) for the pathogen tested except Klebssiella pneumonia (65.5 mg/ml) while the other Senna species have similar minimum inhibitory concentration (MIC). The antimicrobial activity of ethanolic extract of Senna alata was favourably compared with the standard drug, ciprofloxacin. The antibacterial activities of the plant extract could possibly be due to alkaloids and flavonoids. Bioactive substance from these six Senna species can therefore be employed in the formation of antimicrobial agent for the treatment of various bacterial infections or diseases.