A critical aspect of applications in wireless sensor network (WSN) is its lifetime. This issue has received increased attention due to the recent advances in affordable and efficient integrated electronic devices. One approach to extend the wireless sensor network lifetime is to divide the deployed set of all sensors into disjoint subsets of sensor covers, such that each sensor cover can cover all targets and get activated one after another. The sensor network lifetime can be increased by identifying the maximum number of covers and it can be identified through disjoint set cover (DSC). In this paper, a novel improved memetic algorithm (iMA) is proposed to give a better solution to the DSC. The simulation results on various problem instances confirm that improved memetic algorithm significantly outperforms several heuristic and evolutionary algorithms in terms of solution quality, which demonstrates the effectiveness of the proposed algorithm in extending WSN lifetime. © 2014 IEEE.