A number of new benzimidazole derivatives were synthesized by the reaction of benzimidazole with appropriate alkyl halides. The compounds synthesized were intentified by H-1-NMR, Fourier Transformation Infrared (FT-IR) and micro analysis. All new and related compounds studied in this work were screened for their in vitro antimicrobial activities against the standard strains: Enterococcus faecalis (ATCC 29212), Staphylococcus aureus (ATCC 29213), Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853) and the yeasts Candida albicans and Candida tropicalis. Eleven of the compounds were found effective to inhibit the growth of Gram-positive bacteria (E. faecalis and S. aureus) at MIC values between 12.5-400 mug/ml. None of the compounds exhibited antimicrobial activity against Gram-negative bacteria (E. coli and P. aeruginosa) at the concentrations studied (6.25-800 mug/ml). All compounds (except compound 3) were significantly effective against C. tropicalis with MIC values of 6.25-400 mug/ml. Eight of the tested compounds showed an antifungal activity against C. albicans with a range of the MICs between 50 and 400 mug/ml.