In this paper, an accurate approximate solutions for 2 problems arising in heat transfer straight fins are presented using optimal homotopy analysis method (OHAM). The approximated solutions are obtained at different values of parameters for the 2 problems are illustrated, and the fin efficiency is also evaluated. Moreover, the 2 problems are of nonlinear convective-radiative conduction and power-law fin- type. The obtained series solutions of OHAM are compared with the numerical solution (using Mathematica solver) and exact solutions. The square residual error is obtained to verify the accuracy of the presented method.