Abstract: The mesophlly cell structure of Euonymus japonicus ‘Cu Zhi’ in different growing periods in Beijing area was observed under microscope and transmission electron microscope in this paper. The results showed that there were relatively thicker cuticular membranes on the upper and lower edidermise. Thickness of leaves, palisade tissues, spong tissue and cuticular membrane were enhanced gradually from new leaf period to dormant season period. But the spong ration was lower in the same period. In the season of new leaf and growth, starch grains accumulated in chloroplasts and there was a big centure vacuole in the middle of the cell. But in dormancy season, the starch grains disappeared or diminished. The chloroplasts were injured with some abnormal chloroplasts increased plastoglobuli. The chloroplasts were elementary completed under low temperature and the chloroplast lamellar was disconnected. The number of mitochondrion nearby the chloroplasts was increased. The vacuole differentiated into small steeps. It is suggested that the cold tolerance of E. japonicus ‘Cu Zhi’ is related to its well\|developed cuticular membranes and accumulation of strach grains in growth season. E. japonicus ‘Cu Zhi’ can survive in winter in the northern region of China just because of its highly stable structure of mitochondrion and the chloroplasts at low temperature.