Abstract: The bioassay of amitraz on Panonychus citri from Beibei, Zhongxian, Wanzhou, and Changshou was conducted and the LD50 values were 0.014, 0.031, 0.111 and 0.007 mg/L, respectively. Besides, the activities of CarE and AChE from P. citri of different regions were also determined, with corresponding values of 7.78, 3.15, 6.56 and 6.00 nmol/(min·insect) for CarE and 1.07, 0.49, 0.50 and 0.37 nmol/(min·mg) for AChE. Among the four investigated populations, there were significant differences of kinetic parameters for both CarE and AChE. The result of in vitro inhibition study revealed that there were significant inhibitory effects of amitraz on both the two enzymes. The inhibitory effect of amitraz was most obvious at the concentration of 14.67 mmol/L. Under the concentration, the inhibition rates of amitraz on CarE accounted for 65.27%, 73.84%, 81.44% and 88.36%, and those on AChE amounted to 86.84%, 84.36%, 73.32% and 70.85%, respectively.