This study was carried out with an objective to investigate the morpholological and anatomical features, phytoconstituents and antimicrobial potentials of leaves of Cassia fistula Linn. In the present study, the microbial activity of ethanol and petroleum extracts of leaves of Cassia fistula Linn. Was evaluated for potential antimicrobial activity against medically important bacterial strains. The antimicrobial activity was determined in the extracts using agar diffusion method. The antibacterial activities of extracts (25, 50, 100, 250, 500,1000μg/ml) of Cassia fistula were tested against two Gram-positive—Staphylococcus aureus, Bacillus subtilis; two Gram-negative—Escherichia coli, Pseudomonas aeruginosa human pathogenic bacteria; the results showed that the remarkable inhibition of the bacterial growth was shown against the tested organisms. The phytochemical analyses of the plants were carried out and anatomical and morphological study was done. The microbial activity of the Cassia fistula was due to the presence of various secondary metabolites.