In this study, an attempt has been made to fractionalize the governing energy balance equation and Adomian decomposition Sumudu transform method (ADSTM) is used to solve the nonlinear fractional order energy balance equation to find the temperature distribution and to check the efficiency of convective straight fin with temperature dependent thermal conductivity. The thermal conductivity of the fin material is assumed as a linear function of temperature to find the temperature distribution for different values of thermal conductivity and thermo-geometric fin parameters for fractional as well as for integer order energy balance equation. Finally, the obtained ADSTM results has been compared with Variational Iteration Method (VIM) (Coskun et al., 2008) and Numerical method to check the accuracy of the purposed method.