This study describes a cost-effective solution for distribution network protection against lightning surges by selective installation of arresters. To go through this, a probabilistic approach based on IEEE Std. 1410 has been implemented and an optimisation method based on discrete imperialist competition algorithm has been developed. The proposed method considers both technical and economic criteria to achieve the best solution. Consequently, the investment costs and the annual total costs including line investment, maintenance and outage costs are being reduced considering the cost of protective devices. In the optimisation procedure, lightning occurrence and network characteristics as well as transmitted power are considered. The obtained results confirm more efficiency of the proposed method than the conventional methods, from either economical or technical point of view.