Abstract: The main purpose of this paper was to study the change of citrus fruit granulation index and activities of antioxidant enzymes， physiological mechanism of granulation in different sizes of citrus fruit， and to propose comprehensive prevention measures. Satsuma mandarin fruit with different sizes were used to study the effect of fruit size on granulation index and activities of antioxidant enzymes （superoxide dismutase SOD， catalase CAT and peroxidase POD） during storage. The results showed that fruit granulation appeared at 60 d after storage and granulation index increased as storage time prolonged. The fruit weight loss increased during storage and that of large fruit was 8.3% and 22.9% higher than middle fruit and small fruit respectively at 120 d after stora.e. SOD， CAT and POD activities in citrus peel were higher than those in citrus pulp. SOD and CAT activities in citrus peel and pulp decreased gradually during storage， which were the highest in small fruit and the lowest in large fruit among the three sizes of fruits. POD activities decreased gradually， which were the highest in large fruit but were the lowest in small fruit. Satsuma mandarin fruit granulation was a course of peel senescence. Higher POD activities and lower SOD and CAT activities in peel were the main causes for fruit granulation. Antioxidant enzyme activities of large fruit changed most among three sizes of citrus fruits during storage. As a result， it is recommended that selecting middle\|size and small\|size fruit to store could be regarded as an important measure to prevent Satsuma mandarin fruit granulation during storage time．

Key words: Satsuma mandarin, different size fruit, storage stage, granulation, antioxidant enzymes