Abstract: Optimal storage assignment policies are essential for warehouses. The COI-based storage policy concerns with picking productivity, and so products in small batches but with frequent orders would be stored close to the exit of the warehouse. However, the workload imbalance among different aisles reduces the picking productivity in warehouses. Therefore, two advanced COI-based storage policies are advocated, with the aim of reducing workload imbalance among aisles. The problem is formulated by integer programming models with new constraints introduced. The problem is analyzed with real data and results indicate that satisfactory solutions are obtained, as in similar traveling distance, the advanced COI-based storage policies are more effective to reduce workload imbalance.