1) The toughness and the percentage of silica of the leaf blade of rice wich had been water cultured, supplying with various amount of silicic acid, were measured to find their relation to rice blast resistance. 2) KASUGAI solution using tap water was employed for the culture solution. The quantity of silicic acid in tap water used was 13.3 mgm. Si02 per liter. 3) The culture pots were divided into four classes, each supplied with silicic acid, disregarding that of tap water, to contain 0 mgm., 50 mgm., 250 mgm., and 500 mgm. Si02 per liter respectively. 4) The toughness of the leaf blade was measured by needle puncture method using JOLLY'S balance at the motor cell region of the inner half of the blade. And the result was given by gram weight per square millimeter. 5) Summarizing the results thus obtained, a) The resistance of the leaf blade of rice blast is proportional to the quantity of silicic acid given. b) The percentage of silica of the leaf blade is also proportional to the quantity of silicic acid given. c) The toughness of the leaf blade does not increase in proportion to the quantity of silicic acid given.