The paper considers the application of regular parameter perturbation technique to obtain approximate solutions of heat-transfer problems with temperature-dependent thermal properties. For pure conduction, linearly varying thermal conductivity and heat capacity are considered and two examples are solved. Next, a conducting-convecting fin is treated with convective heat-transfer coefficient proportional to ( ΔT) ε with ε = 0·25 for fin cooled by natural convection and ε = −0·25 for fin heated by laminar condensation. Finally, a two-parameter perturbation is used to solve for temperature distribution in a conducting-convecting-radiating fin with temperature-dependent thermal conductivity. On comparing the perturbation solutions with corresponding numerical solutions, the accuracy is found to be good.