Antimicrobials derived from plants have been receiving increasing attention in recent years. Antimicrobial activities of a number of phytochemicals have been reported. Many antibiotics are ineffective against several pathogenic organisms. About 90% of S. aureus, E. coli, P. aeruginosa, S. pyogenus, C. albicans, A. niger and A. clavatus have resistance against many antibiotics. In the present study, the effect of R-spirit, benzene and water extracts of a medicinal plants cassia occidentalis has been tested against β-Lactum resistant strains of S. aureus, S. pyogenus, C. albicans and E. coli, P. aeruginosa A. niger and A. clavatus in presence of antibiotics such as gentamycin, ampicilin, ciprofloxacin, chloramphenicol, norfloxacin, nystatin and greseofulvin. The alcoholic extract has shown the maximum antimicrobial activity and the active ingredients are found to be 4, 5-dihydroxy-9, 10-dioxo-4a, 9, 9a, 10- tetrahydro-anthracene-2-carboxylic acid and 1, 3, 8-trihydroxy-6-methyl-anthraquinone which are characterized by NMR, FTIR and Mass spectroscopy. The Minimum Inhibitory Concentration (MIC) for antibacterial activity of the compound was found 6.25 μg/mL against the β-lactum resistant strains of S. aureus and MIC for antifungal activity was found 50 μg/mL.