This study presents the application of storage assignment and human error improvement model in warehouse management to the case study of automobile seat manufacturers. The objectives are to improve the efficiency and accuracy of the order picking (OP) process in companies. To improve the efficiency of the OP process, capacity decision analysis and an optimization method using linear programming are used to perform storage assignments of raw material in the warehouse. The human error improvement model is then used as a method to reduce human error that occurs in the OP process and increase its accuracy. The three scenarios of storage assignment result in the total OP time for one month in scenario 1, scenario 2, and scenario 3 is 417.9 hours, 288.6 hours, and 255.5 hours respectively. Improvement actions that have the highest effectiveness to difficulty ratio were conducting spreadsheet training for data recording purposes, implementing a FIFO card system with different shelf lines for new goods and old goods after the addition of capacity, and making a large map of item raw material placement in the warehouse.