The purpose of this research is to forecast the prices of the agricultural products by using Gray theory. In this research, Adzuki Beans is our research object. We use four consecutive months data to forecast the price of Adzuki Beans next month. After our calculation, we find that the forecasted price is close to the real price. It implies that Gray theory is convenient to forecast prices of agricultural products. We hope that farmers, wholesalers, and government officers can get benefits in determining the scale, pricing, and setting policies from the results of Gray theory.