The Padmakar-Ivan (PI) index is a Wiener-Szeged-like topological index which reflects certain structural features of organic molecules. Each structural feature of such organic molecule can be expressed as a graph. In this paper, we study the PI indices for some special graphs, such as Ir(Fn), Ir(Wn), ~ n F , ~ n W , Ir( ~ n F ) and Ir( ~ n W ).