To understand the relationship between lodging resistance and chemical component contents in culms and leaf sheaths of rice,the physical strength and maximum bearing capacity of culm,and the contents and amounts of potassium (K),silicon (Si) and soluble sugars in culms and leaf sheaths were investigated using four japonica rice varieties with different lodging resistance characteristics during grain filling.There were significant differences in the total amounts of K,Si and soluble sugars in culms and leaf sheaths among the tested rice varieties.The difference in the total amount of Si was greater than that of K or soluble sugars.The physical strength and maximum bearing capacity of culm continuously decreased from heading to ripening,with a rapid decrease at the dough stage.However,the contents and total amounts of K and Si in culms and the Si content in leaf sheaths gradually increased and an accumulation of K and Si in culms was exhibited,whereas the content and total amount of K and the total amount of Si in leaf sheaths gradually decreased and an exportation of K and Si in leaf sheaths was presented.The physical strength was positively and significantly correlated with the total amounts of K and Si in culms during grain filling except that at the heading stage,the total amount of soluble sugars in culms at the heading and milky stages,the total amounts of Si and soluble sugars in leaf sheaths at the heading stage,the total amount of K in leaf sheaths at the heading and milky stages,and the maximum bearing capacity during grain filling.It is suggested that the lodging resistance of japonica rice would be improved by increasing the amount of soluble sugars in plants at the early filling stage,and enhancing the amount of Si in plants during grain filling through topdressing Si fertilizer at the early filling stage.