Abstract: The popularity of wireless sensor have been increased in recent time due to growth in MEMS technology. Wireless sensor networks made up of hundreds or thousands of sensing nodes. It is necessary to make these nodes cheap and energy efficient. Most of the attention given to the routing protocol for energy efficient solutions. LEACH has been widely accepted WSN routing protocol for its energy efficiency. Evolutionary algorithm (EA) also used by researcher to resolve cluster based protocol in WSNs. The main goal of EA based clustered routing protocol is to dynamically form clusters in WSNs such that the use of energy resources of the network is minimized and prolong network lifetime. Aim of this paper is to ease the difficulty of undesirable behaviour of EA by formulating a new fitness function by introducing the concept of residual energy. Simulation shows that modified evolutionary routing protocol (ERP-M) prolong the network lifetime and saved more energy as compared to LEACH, SEP and ERP.