Two-spotted spider mite, Tetranychus urticae Koch, is most economically important pest on crops in Korea. Control of spider mite populations is primarily dependent upon the acaricides. Pyridaben, belongs to METI (mitochondrial electron transport inhibitor) group, was first registered in Korea in 1992. Field populations of T. urticae collected from apple trees and strawberries appeared to be highly resistant to pyridaben in spite of its short-term use. A strain of pyridaben resistant T. urticae collected from apple orchard in 2002 was further selected with pyridaben 20% WP for 27 generations at a selection pressure of 30-50% mortality (PR-27 strain). Resistance and cross-resistance levels of the PR-27 strain to 16 acaricides were determined by a spray method. The PR-27 strain was extremely resistant to pyridaben (Resistance ratio(RR) 86). The strain exhibited positive cross-resistance to fenpyroximate (RR >12), fenazaquin (RR >7.8) and tebufenpyrad(RR >8.7). The PR-27 strain showed low levels of cross-resistance to fenpropathrin, abamectin, monocrotophos, dicofol, chlorfenapyr, azocyclotin and fenbutatin oxide. Synergist experiments with different metabolic inhibitors revealed that piperonyl butoxide(PBO) had the low effect on the efficacy of pyridaben. Also there was no significant difference in mixed function oxidase(MFO) activities between the S and PR-27 strains(RR 0.6). Iprobenfos(IBP) rolling as inhibitor of carboxylesterase showed low inhibition to PR-27 mite and esterase activity of resistant strain was lower than that of susceptible one(RR 0.7). It was proposed that metabolic detoxification by esterase and p450 oxidase did not play major role in mechanism of resistance to pyridaben in T. urticae.