Abstract: Activator protein is a kind of protein elicitor extracted from many plant pathogenic fungi. In order to understand the resistance induction of activator protein of Monilinia fructicola, activator protein was extracted from M. fructicola mycelium by boiling-water-bath and centrifugation and sprayed on leaves of strawberry seedlings. The activity of some defence enzymes were detected and the results showed that the activity of PAL increased in 0 ~ 18 h, and reached the peak at 18h with a peak value 40.7% higher than control; the activity of POD and PPO increased rapidly in 0 ~ 6 h, and reached the peak at 6h with peak values of POD 126.2% higher than control and PPO 62.9% higher than control. The activity of β-1, 3-glucanase and exo-chitinase increased after treat with activator protein of M. fructicola.