A method and a calculation formula for determining the thermal conductivity of solids under constant radial heat flow conditions by use of the Peltier and Joule effects is presented. The instrument constant and coefficient of thermal disequilibrium have been determined using four standard samples with known thermal conductivity : quartz glass, plexiglass, teflon and polyethylene. The reproducibilities of measurements for the heat of thermal disequilibrium in the investigated sample were less than 0.50% and the amount of heat flux through the wall of the investigated cylinder was within 0.07%. The standard deviation, relative error and accuracy of the thermal conductivity determined using this method were 1.8%, 0.22% and 5%, respectively. The thermal conductivities of quartz glass, plexiglass, polyethylene and teflon at 298 K were measured and it was found that the heat of thermal disequilibrium was the principal factor affecting the magnitude of the thermal conductivity of these samples.