In this paper a new approach will be used for optimal coordination of directional over current (DOC) relays based on genetic algorithm. In this approach, optimal operation characteristics and also optimal current setting and time setting of each OC relays will be determined simultaneously. Also, a new objective function will be used which is different from ordinary methods such as simplex, two phase simplex, dual simplex. Improvement of selectivity and speed of the protection system, obtaining the absolute optimal point of the optimization problem are the specifications of the proposed approach. Numerical results obtained with the proposed method for a real power system are presented.