Relationships between the non-structural carbohydrate (C) and nitrogen (N) content of the leaves and roots and the productivity in consecutive seasons of 16-year-old satsuma mandarin (Citrus unshiu, Marc. cv. Aoshima) trees were investigated. Flower formation in the following season had the highest positive correlations with both leaf and root C content in November (maturation period). The correlations with root C in February (dormant period) in each season were also high, but they became slightly lower when the data for the two seasons were combined. Nitrogen content did not appear to be important for flower formation. Fruit set after June drop in the following season had the highest positive correlation with root C content in February. Multiple regression analysis showed that the root N content in February contributed greatly to fruit set. These nutritional factors were somewhat less effective than productive factors in the current season for estimating flower formation in the following season, but they were much more effective for evaluating fruit set after June drop. These results show that reserved nutrients can be effective predictors of fruit productivity in satsuma mandarin trees.