The development of drug resistance as well as appearance of undesirable side effects of certain antibiotics has lead to the search for new antimicrobial agents mainly from plant extracts with the goal to discover new chemical structures, to overcome these disadvantages. The research was therefore carried out to evaluate the in-vitro antibacterial activity of Cassia occidentalis flower extract. The clinical bacterial isolates, Klebsiella pneumoniae, Staphylococcus aureus, Streptococcus pneumoniae and Pseudomonas aeruginosa were subjected to antibacterial susceptibility test using agar well diffusion method. The results showed that all the extracts had activity against Klebsiela pneumoniae at a concentration between 30 – 90mg/ml. There was no antimicrobial activity exhibited against the other three test organisms. The Minimum Inhibitory Concentration ranged between 35 – 55mg/ml for water extract and 25 – 55mg/ml for chloroform extract. The Minimum Bactericidal Concentration was 55 mg/ml by both water and chlorofrom extract . The phytochemical analysis of the flower extracts revealed the presence of tannin, flavonoid, anthroquinone, saponin, carbohydrates, and cardiac glycoside. C. occidentalis flower extract might therefore be used to treat Klebsiella associated illness such as pneumonia and bronchitis.