The susceptibilities to insecticides and acaricides, as well as carboxylesterase (CarE), cytochrome P450 monooxygenase (P450) and glutathione S-transferases (GSTs) activities were evaluated in a susceptible (SSS) and an unsusceptible strain (RSS) of Stethorus gilvifrons (Muls.) (Col.: Coccinellidae). Synergism studies using S, S, S-tributylphosphorotrithioate (DEF), piperonyl butoxide (PBO) and diethyl maleate (DEM) in combination with at a discrimination dose (similar to LD20) of selected pesticides were also conducted to test for possible physiological mechanisms. In addition, the insensitivity of acetylcholinesterase (AchE) to the inhibitors, paraoxon and pirimicarb, is also determined. Compared with SSS, tolerance ratios of RSS, as indicated by LC50 values, was calculated 2.1, 11.2, 6.7, 1.7, 1.6 and 2.3-fold, respectively, for abamectin, bifenazate, chlorpyrifos, cyhexatin, hexythiazox and lambda-cyhalothrin. Thus, the field collected resistant S. gilvifrons population were tolerant at medium level to four compounds. CarE activity was significantly higher in RSS than in SSS, 1.5-fold for alpha-naphthyl acetate and 4.3-fold for beta- naphthyl acetate. Also significant enhanced GSTs activity were determined in RSS using two substrates, 1-chloro-2,4-dinitrobenzene (4.3-fold) and 2,4-dinitro-1-iodobenzene (1.4-fold), compared with SSS. Inhibition kinetics revealed that AchE from RSS was 2.5-fold more insensitive to inhibition by 1mM primicarb than AchE from SSS. The disparity in susceptibility to these pesticides in the predator populations were due to the responsibility of multiple physiological mechanisms, including elevated CarE, GSTs and P-450 enzymes activities.