Disease susceptibility of a silicon（Si）uptake-deficient mutant ls0i1 originating from cv. Oochikara of rice（wild-type）was investigated. When the mutant and wild type rice plants at three-leaf stages were inoculated with Magnaporthe grisea, blast lesion formation was rapidly enhanced in the leaves of the mutant lsi1, as compared to that in wild type rice cv. Oochikara. Si concentration in leaves of lsi1 was lower than that of cv. Oochikara and its percentages per dry weight in lsi1 and Oochikara were 1.2±0.6 ％ and 4.6±1.2 ％, respectively. This study suggests that Si uptake deficiency is involved in enhanced susceptibility of lsi1 mutant to seedling blast.