To contribute to the development of new integrated practices for the control of soilborne diseases, the relation between the development of bacterial wilt, a serious soilborne disease induced by Ralstonia solanacearum, and Ca nutrition in tomato (Lycopersicon esculentum Mill.) seedlings was investigated. Increased Ca concentrations in the nutrient solution reduced the disease severity in the seedlings of resistant cultivars, and decreased the populations of the pathogen in stems. This Ca-dependent resistance was also observed in susceptible tomato seedlings grafted onto rootstocks of a highly resistant cultivar. The resistance was affected by the Ca concentration after infection with the pathogen, but not before infection, suggesting that the Ca concentration in the cell walls before infection might not be directly involved in the Ca-dependent resistance. When varietal differences in the resistance and nutrient uptake by the seedlings were examined, highly resistant cultivars were characterized by a high Ca uptake. However, the differences in Ca uptake might not be related to the expression of the resistance, based on the results of experiments using mutually grafted seedlings of cultivars differing in resistance. Application of composts with various Ca concentrations reduced the disease severity, and the degree of reduction was correlated with the increase of the Ca uptake in shoots. These results indicate that the resistance of tomato to bacterial wilt is markedly affected by Ca nutrition of the host.