Lodging is one the important factors that limit rice yield and reduce rice grain quality. The study is conducted to determine suitable concentration of Calcium, Prohexadione-Ca (Pro) solution on height, hardness of rice stem and lodging resistance of Hananomai and Koshihikari varieties. The experiment was done in Winter-Spring crop in Thoai Son district, An Giang province. It was designed in random complete block factor and included 16 treatments which is combination of the 8 forms of treating Calcium and Pro (0, Ca 150, 200, 250 ppm, Pro 30 ppm, Pro 30 ppm + Ca 150, 200, 250 ppm) and two rice varieties which repeated 3 times. Results recorded as follows application of Pro 30 ppm in combination with calcium 200 ppm related to the reducing plant height and cell length, shorting length of internode, increasing thickness and hardness of rice stem. Therefore, reduced lodging to contributed to increased yields.