A new series of 10-methyl-6-oxo-5-arylazo-6,7-dihydro-5H-[1,3]azaphospholo[1,5-d][1,4]benzodiazepin-2-phospha-3-ethoxycarbonyl-1-phosphorus dichlorides 11a-p has been synthesized and evaluated as antimicrobial agents. Structures of all the synthesized compounds were established on the basis of elemental analysis and spectroscopic data. Quantitative structure-activity relationship (QSAR) investigations were applied to find out the correlation between the experimentally evaluated activity with various parameters of the compounds studied. QSAR equations showed that the molecular refractivity correlates significantly with the antimicrobial activity.