The damage of rice stem rot (Leptosphaeria salvinii Cat.) was decreased when sheathes of lower-part of rice plant were stripped during the season from milk stage to two weeks before harvest. The same results were obtained by the reinoculation experiments with sclerotia of the fungus just after the sheath removing. Protein nitorogen and chlorophyll contents were increased in some extent by the sheath removing, when analytically compared of carbohydrate, nitrogen, chlorophyll and reserved starch contents of lower-parts of culms with that of not treated culms. It is concluded that the sheath stripping of the lower-part of rice stem acts on one hand to remove the pathogen existing as the invasion source in the diseased spot of sheath and on the other hand to delay the maturity of rice stem, consequently the latter is able to avoid the severe damage.