In a recent paper by Sobhan Mosayebidorcheh and Taha Mosayebidorcheh, "Series solution of convective radiative conduction equation of the nonlinear fin with temperature dependent thermal conductivity", Int. J. Heat Mass Transfer 55 (2012) 6589-6594, the temperature distribution and efficiency of convective-radiative straight fins were studied. Although the energy equation has been written correctly and therefore the obtained temperature field is correct, a significant mathematical error is identified on the fin efficiency. The present comment proves that the proposed fin efficiency in that paper is invalid, derives its correct form and shows that such an error may strongly affect the results. (C) 2013 Elsevier Ltd. All rights reserved.