Abstract: Abstract: Influences of low dose short wave ultraviolet (UV-C) on disease resistance in apple and its action mechanisms were studied for providing scientific basis of UV-C application in apple storage. The test material was 'Red Fuji' apple and common ultraviolet germicidal lamp with wavelength of 254 nm was used as the radiation source. The apples were irradiated with the radiation dose of 0, 2.5, 5.0, 7.5, 10.0, 12.5 kJ/m2, respectively. Then we conducted the experiment that the influence of optimal dose UV-C on penicillium disease resistance under low temperature. At the same time, we studied the resistance of apple with appropriate dose of UV-C treatment to Botrytis cinerea at normal and low temperature. Apple fruits treated with optimal dose of UV-C were stored under the condition of 20℃ and 0℃, respectively. Total phenol content, malondialdehyde (MDA) content and activities of protective enzymes (polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), superoxide dismutase (SOD), peroxidase (POD)) were measured periodically during storage. There was a significant difference between all dose of UV-C treatments and control under room temperature in disease incidence and decay diameter, and the disease resistance of apple enhanced with increasing dose of UV-C at the beginning. However, the resistance of apple to postharvest decay decreased with UV-C above 7.5 kJ/m2. Therefore 7.5 kJ/m2 was the optimum dose in this study. The treatment with optimal dose of UV-C has good effects on disease resistance in harvested apple inoculated Penicilium expansum or Botrytis cinerea under low temperature. Under room temperature, the disease incidence of UV-C treated apples was 66.7%, significantly lower than that of control (90%) at 4d after inoculated Botrytis cinerea. The results showed that apple fruits resistance to different diseases increased with UV-C treatment. Treatment with UV-C 7.5 kJ/m2 can effectively reduce the accumulation of MDA, protect cell membranes, increase the total phenolics accumulation and enhance disease resistance. Under the condition of room temperature, total phenolics of UV-C treatment apples was significantly higher than that of control at 7 d (the treatment is 1.18 times of control).; MDA content of treated fruits was lower than that of control at 2 d and 7 d. Total phenolics of UV-C treated apples was higher than that of control after 37 days storage at low temperature. And MDA content of treatment group was lower than that of control throughout the storage. PAL and PPO activities of fruits treated with 7.5 kJ/m2 UV-C were higher than that of control during the whole storage period at room and low temperature. SOD and POD activities were significantly increased especially at 2 d and 7 d under room temperature. We concluded that UV-C treatment can effectively suppress the occurrence and expansion of Penicillium at room temperature, and the optimal dose of UV-C in this research was 7.5 kJ/m2. The activities of protective enzymes and the disease resistance of apple were improved by 7.5 kJ/m2 UV-C treatment. Suitable dose of UV-C can be used for postharvest apple to increase the disease resistance and prolong the storage period.