A series of 17 hydrochlorides of piperidinylpropyl esters of alkoxy-substituted phenylcarbamic acids with the alkoxy group in position 2, 3 or 4 on the phenyl ring, and basic substituents attached to the moiety in position 3, were evaluated for in vitro antimycobacterial activity against the strains of Mycobacterium tuberculosis, M. kansasii and M. avium. To describe the structure-antimycobacterial activity relationships (QSAR), an approach based on the Free-Wilson method was employed to express the differences between individual moieties (including propyl and ethyl). The change of ethyl to propyl moiety increases the activity to M. tuberculosis but decreases the antimycobacterial activity to all potentially pathogenic strains under study.