In this paper, designing an output feedback controller is investigated based on Lyapunov-Krasovkii stability theorem and linear matrix inequality. The goal is to achieve preliminary identical synchronization for synchronizing identical chaotic neural networks. The error convergence of the slave system is the significant advantage of the proposed technique. Also, complete synchronization is achieved with this method clearly. Simulation results of the proposed method for a well- known chaotic neural network show the efficiency of the proposed method.