Abstract: In order to clarify the control efficacy and control mechanism of fungicides with different dosages and control stages on rice false smut, we studied the control efficacy of two fungicides with three dosages and eight stages on rice false smut ofI ndica-japonica hybrid cultivar‘Yongyou 12’. The results showed that the control efficacy of the two fungicides at proposed dosages was better, and the efficacy increased along with the dosage increase. But the dosage was not the key factor to the control efficacy, except that the control efficacy of XI’AO at 300 g/hm2 was significant lower than those of the other dosage treatments. The two fungicides had some efficacy at 20 days before the rupturing stage, and the efficacy increased with the control stage which was close to the bloom stage. Nevertheless, the control efficacy began to reduce after rupturing, especially XI’AO declined rapidly after the full heading stage. In conclusion, the crucial stage of infecting rice false smut for cultivar‘Yongyou 12’was the bloom period, so efficacious and long-acting fungicides must be used before rupturing stage to control rice false smut.