Finding a series expansion, such as Taylor series, of functions is an important mathematical concept with many applications. Homotopy perturbation method (HPM) is a new, easy to use and effective tool for solving a variety of mathematical problems. In this study, we present how to apply HPM to obtain a series expansion of functions. Consequently, this article presents an alternative approach, contrary to the traditional Taylor series method, for finding a series expansion of functions. The developed approach can be incorporated in an undergraduate course. (Contains 1 figure and 4 examples.)