Experiments were conducted to test the effects of pure O2 on browning of litchi (Litchi chinensis Sonn. cv. Huaizhi) fruit in relation to the changes in ultrastructure of peel tissue. Litchi fruits were kept in air or pure O2 for 6 days at 28℃. Browning index and relative leakage rate were determined, and the changes in cellular ultrastructure was observed. Application of pure O2 significantly prevented browning and delayed the increase of membrane permeability in litchi fruit pericarp. Exposure of litchi fruits to pure 02 resulted in a delayed breakdown of cytoplasm and valdous organelles， which might account for the maintenance of cell membrane integrity． It is suggested that the partial protection from breakdown of cellar integrity of litchi fruits by pure O2 treatment could reducebrowning.