1-(Dialkylaminomethyl)-2-(p-substituted phenyl)-5-substituted benzimidazole derivatives 1 have been synthesized by reacting 2-phenylbenzimidazole derivatives with formaldehyde and a secondary amine. The derivatives of 2-phenylbenzimidazole were obtained by reacting the bisulfide addition product of substituted benzaldehydes with 4-substituted-o-phenylenediamines. Their structures were confirmed by microanalysis, IR and NMR spectral analysis. Antimicrobial activity of the compounds was investigated by the microdilution susceptibility test in Mueller-Hinton Broth and Sabouraud Dextrose Broth was used for the determination of antibacterial and antifungal activities. Test organisms: Staphylococcus aureus ATCC 29213 and Enterococcus faecalis ATCC 29212 as Gram-positive bacteria, Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853 as Gram-negative bacteria, and Candida albicans, C. parapsilosis, C. stellatoidea as yeast-like fungi. Compounds 1a, 1b, 1c, 1e and 1i showed slight to moderate activity against all microorganisms. Compound 1g showed the highest activity. It was found more potent than streptomycin against Enterococcus faecalis and Pseudomonas aeruginosa.