Abstract: The purpose of this study was to investigate the effects of different proportions of aged paddy rice replacing corn on the physicochemical properties, pelleting performance, and product quality of corn-soybean meal mixed powder. The processing parameters were then optimized under different replacement ratios. The best replacement ratio and process parameters were obtained after optimization. The aged paddy rice, corn, and soybean meal were used as the feed raw materials and then ground by a hammer mill with a sieve diameter of 2 mm. These powders were mixed evenly, according to the given proportion. Three samples of mixed powder were randomly taken and stored in a sealed bag, in order to determine the physical and chemical properties. Box-Behnken design was used in the experiment. A total of 17 groups of pelleting groups were constructed with the aged paddy rice replacement ratio, the conditioning temperature, and the conditioning time as the independent variables, while the feed pellet durability index, pelleting rate, and power consumption per ton as the dependent variables. A pellet mill was also used in the test, where the diameter of the die hole was 3 mm and the length-diameter ratio was 10:1. The pellet feed samples were taken to qualify the process parameters of the conditioner and pellet mill. The working parameters were also recorded during production. The physicochemical properties of mixed powder were measured, such as angle of repose, angle of frictional, bulk density, tap density, compressibility, water absorption index, water solubility index, swelling power, viscosity characteristic value and pelleting characteristics, such as pellet durability index, pelleting rate and power consumption per ton. Three independent variables were then optimized. The results showed as follows: 1) In properties of the material, the angle of repose, the angle of friction, bulk density, and tap density decreased significantly (P<0.05) with the increase of the proportion of aged paddy rice replacing corn; The water absorption, peak viscosity and holding viscosity increased first and then decreased, while the pasting temperature and final viscosity increased significantly (P<0.05). 2) In process parameters, the pelleting rate first increased and then decreased, and the power consumption per ton and pellet durability index gradually increased (P<0.05). The power consumption per ton decreased first and then increased significantly (P<0.05). The pellet durability index first increased and then decreased gradually. Furthermore, the pelleting rate gradually increased with the extension of conditioning time, and the power consumption per ton decreased first and then increased. The pellet durability index first increased and then significantly decreased (P<0.05). 3) The response surface variance analysis showed that the descending order was obtained: the replacement ratio of aged paddy rice > conditioning temperature > conditioning time, representing the effects of each factor on the pelleting characteristics. 4) The optimization and prediction of process parameters showed that the adjustable range of conditioning temperature increased first and then decreased with the increase of the proportion of aged paddy rice replacing corn, whereas, the conditioning time decreased first and then increased. The aged paddy rice instead of corn in feed processing can significantly improve the product quality and the energy consumption of pelleting.