Abstract: Substituted piperidyl benzimidazolinone derivatives exert a wide range of pharmacological effects according to different substituents in position-1 of piperidine ring. These include tranquillizing, antihypertensive and analgesic activities and so on. The syntheses and analgesic activities of a series of substituted piperidyl benzimidazolinone derivatives as potential analgesics are reported in this paper. In mouse hot plate test most of these compounds showed analgesic activity and 1-1-1-(ptolyl)-ethyl-4-piperidyl-3-(2-cyanoethyl)-2-benzimidazolinone(I_h) was found to be the most potent, with a potency more than 500 times that of morphine. Introduction of a methyl group in position-3 of the piperidine ring markedly decreased the analgesic activity.