In this paper, a new approach to maintenance scheduling of generating units (MSU) in competitive electricity markets is presented. The main contribution of this study can be focused on modeling a game-theoretic framework for the MSU problem to analyze strategic behaviors of generating companies (Gencos). The MSU problem is formulated as a dynamic noncooperative game with complete information. The player corresponds to the profit maximizing individual Genco, and the payoff of each player is defined as the profit from the energy auction market. The optimal strategy profile is defined by the Nash equilibrium of the game. Numerical results for two-Genco systems are used to demonstrate the basic ideas of the proposed scheme, and large-scale IEEE reliability test systems are also considered to show the applicability of the proposed framework. The results obtained indicate that maintenance schedule can be one of the crucial strategic behaviors whereby Genco maximizes his profit in a competitive market environment.