Immature Citrus unshiu contains large amounts of various physiologically active substances compared to mature Citrus unshiu. They are also known to exert various biological effects such as antioxidant, anti-inflammatory, and anti-obesity. However, the active ingredients that express functionality generally have disadvantages under external environments such as light, heat, and pH. Therefore, we conducted microencapsulation using a spray drying technology to protect the active ingredients of immature Citrus unshiu concentrate (ICUC). We further strived to establish optimal processing conditions using the Box-Behnken design method of response surface methodology (RSM). In order to develop the optimized immature Citrus unshiu powder using RSM, the inlet temperature (X1), aspirator power (X2), and maltodextrin concentration (X3) were set as independent variables, and quality characteristics such as dry yield (Y1), water content (Y2), water activity (Y3), total phenolic content (Y4), and particle size (Y5) were set as dependent variables. The P values of the Y1, Y4, and Y5 models were all less than 0.0001, and the determination coefficient (R 2 ) was 0.9541, 0.9767, and 0.9799, respectively, confirming the model's suitability and reliability. The maximum value of dry yield (15.75%) and minimum value of water activity (0.079) and particle size (346.44 nm) were obtained under the optimal conditions of inlet temperature 200°C, aspirator power 99.75%, and maltodextrin concentration 20%. In conclusion, we believe that this study will help establish optimal spray drying conditions for microencapsulation of ICUC and other fruit and vegetable extracts.