Red spider (Tetranychus urtica) is one of many plant species feeding mites, which cause large agricultural losses. Garlic oil was investigated as acaricidal source to evaluate its ability to protect plants from mite injury. The red spiders were spread on green bean seedlings for one week then the plants were sprayed with different concentrations of garlic oil (50,250,1000,2000,5000 ppm). The results showed that garlic oil showed an acaricidal activity against red spider in dose and time dependent manner. Also, high and low concentrations of   garlic oil inhibit acetyl cholinesterase (AChE), while protease activity was declined due to treatment with 1000, 2000 and 5000 ppm garlic oil. On the other hand, the concentration of 50 and 250 ppm increase the red spider protease activity. We can conclude that the garlic oil exhibited acaricidal activity against red spider. The observed acaricidal effect of garlic oil is highly correlated with the inhibition of acetyl cholinesterase (AChE) and protease activities.