Methanol and aqueous extracts of four plant species namely Nigella sativa, Acorus calamus, Myristica fragrans and Hemidesmus indicus traditionally used in Indian folklore medicine for the treatment of various bacterial and fungal infections were investigated for antimicrobial activity against pathogens viz Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus sp., Escherichia coli and Candida albicans by well diffusion and minimum inhibitory concentration (MIC) methods. Comparative study of the antimicrobial activity of the plant extracts and its synergistic effect with antibiotics was carriedout. Maximum zone of inhibition was observed against S. aureus, E.coli, Bacillus sp and P. aeruginosa by methanol extracts of Nigella sativa and Hemidesmus indicus. C albicans showed susceptibility to methanol extracts of Acorus calamus and Hemidesmus indicus. Phytochemical analysis of methanol and aqueous extracts of Nigella sativa and Hemidesmus indicus revealed the presence of alkaloids, flavonoids, triterpenes, polyphenols and sterols. Both the active extracts were separated by adopting analytical thin layer chromatography. Totally two spots were observed for Hemidesmus indicus and Nigella sativa showed only one spot, when chloroform: methanol (70:30) used as a solvent system. The active fraction was determined by bioautography by using S. aureus as test organism. Only Nigella sativa extract alone showed synergistic effect with antibiotics and the positive results were showed by S. aureus and E. coli. The results provide justification for the use of the plants in folk medicine to treat various infectious diseases.