The scope of this study is to determine effective order picking routes in warehouses considering minimization of energy consumption and to show a way for applying green principles in warehouse operations. Order batching is applied for increasing efficiency of order picking process. Because of close relation to the performance of the picking operation, storage assignment policies are also discussed for minimization of energy consumption. A genetic algorithm (GA) is proposed as a solution approach for order batching and routing optimization in order to minimize energy consumption. Remainder of this paper is organized as follows. Section 2 provides literature review about order picking, storage assignment and green warehousing. In Section 3, the definition of the studied problem is presented. In Section 4, the proposed solution methodology is described. Section 5 provides numerical experiments and computational results. Finally in Section 6, conclusions are summarized.