Genetic algorithms (GAs) serve as a class of powerful tools to search for an effective multicast routing scheme among multiple cluster header nodes,which strongly affects the lifetime of two-tiered Wireless sensor networks (WSNs).This paper proposes a novel Genetic algorithm (GA) with a new crossover mechanism called Leaf crossover for the multicast routing among upper tier nodes in two-tiered WSNs,which outperforms the existing popular tree-based GAs by not requiring the global network link information,encoding/decoding or repair operations.Our simulation study indicates that the proposed algorithm could prolong the lifetime of multicast service,increase the packet delivery ratio as well as converge fast by comparison with existing GAs.