Abstract: Taking Chinese cabbage ‘Jinguan’ as the test material, the different concentrations(50-250 μmol·L^-1) of MeJA were applied to the roots of Chinese cabbage under clubroot stress, the effects of MeJA on seedlings growth, defense enzymes, osmoregulation substances and related defense gene expression were studied, in order to provide reference basis for the prevention and treatment of Chinese cabbage clubroot by exogenous MeJA.The results showed that exogenous MeJA could significantly reduce the disease index which was negatively correlated with MeJA concentration, and also significantly decrease MDA and osmoregulation substances contents, especially at the concentration of 100 μmol·L^-1.While, the growth of cabbage seedlings was inhibited when applying more than 150 μmol·L^-1 MeJA.Additionally, exogenous MeJA application increased chlorophyll content and antioxidant enzyme activity in Chinese cabbage leaves, as well as up-regulated disease-related protein genes PR-1 and PR-3,so that the resistance of Chinese cabbage seedlings to clubroot was improved.Through comprehensive analysis, application of 100 μmol·L^-1 MeJA could effectively promote the resistance of Chinese cabbage seedlings to clubroot most.