The present article investigates heat transfer phenomenon in an aerospace radiating fin, analytically. Radiating extended surfaces are widely used to enhance heat transfer between primary surface and the environment. The performance of such a surface is significantly affected by variable thermal conductivity; especially in the case of large temperature differences happened in the actual aerospace applications. To study the effect of thermal conductivity variation, linear length-dependent function of thermal conductivity, is considered. In this study, two newest and popular analytical methods, differential transform method and optimal homotopy asymptotic method are used to evaluate the temperature profile and efficiency of radiating fin. For this purpose, after deriving and dimensionalizing the radiating fin heat transfer equation and briefly introducing these two methods, they are employed to solve the radiating fin problem. The obtained results are compared with the numerical ones to verify the accuracy of the proposed methods and choosing the better one between them, which is exclusive for this paper. Then, the effects of thermal conductivity and thermo-geometric radiating fin parameter on temperature profile and fin’s efficiency are completely discussed, which can help materials science researchers to design more compact and efficient radiating fin for using in aerospace and satellite applications.