The efficacy of submicron chitosan dispersions (SCD) on Alternaria alternata rot of the ‘Lingwu changzao’ jujube (Zizyphus jujuba Mill. cv. Lingwu changzao) fruit and possible mechanisms involved were investigated in this study. When jujube fruit at the preharvest stage were sprayed twice with SCD (10 mg/ml) water solution and then natural infections were allowed to develop, there was a significant reduction in disease incidence and lesion index compared to control fruit during storage period, and similar results were obtained from postharvest fruit inoculated with the Alternaria rot pathogen. Scanning electron microscopy of the pathogen revealed that hyphae and spores were damaged and deformed when growing on the surface of fruit pretreated with SCD or CHO. The slowed softening of jujube fruit resulted from the protopectin content increasing compared with the control. Furthermore, SCD sprays inhibited cell wall hydrolysing enzymes, pectinase activity was decreased, and the increase in cellulase activity was postponed (from 30 days to 45 days).It was concluded that preharvest application of SCD was a more effective alternative to conventional chitosan for preventing postharvest from Alternaria rot of ‘Lingwu changzao’ jujube fruit.