The paper presents the results of experimental study of the influence of the doping agent (acid) nature on the conductivity, Seebeck coefficient, and thermoelectric power factor of composite material based on multilayer carbon nanotubes coated with polyaniline. Polyaniline was deposited on carbon nanotube surfaces by heterophase synthesis (in-situ polymerization), by oxidative polymerization of aniline in the presence of nanotubes dispersed in the reaction medium. Hydrochloric, camphorsulfonic and dodecylbenzenesulfonic acids were used as doping agents. The effect of temperature on the conductivity, Seebeck coefficient and thermoelectric power factor of the investigated composite materials has been studied in the range from 300 to 410 K. Comparison of the influence of the acid volatility on the changes in these parameters in the heating-cooling cycle allowed us to conclude that the decrease in conductivity and increase in the Seebeck coefficient when heating composites doped with different acids is caused by the acid removal from the samples.