In this paper we propose a new Power Efficient Clustering Protocol (PECP) for prolonging the sensor network lifetime. Homogeneous clustering protocols assume that all the sensor nodes are equipped with the same amount of energy and as a result, they cannot take the advantage of the presence of node heterogeneity. Adapting this approach, we propose a new protocol named PECP (Power Efficient Clustering Protocol) to improve the stable region of the clustering hierarchy process using the characteristics parameters of heterogeneity, namely the fraction of powerful nodes (with more energy) more suitable to become a cluster head. Intuitively, powerful nodes have to become cluster heads more often than normal nodes. The performance of the PECP via computer simulation is evaluated and compared with other clustering algorithms. It has been found that PECP prolongs the sensor network lifetime.