The LC values of Tetranychus urticae Koch BE populations collected from Antalya province in bean greenhouse on May 2003 were determined using by spray tower - petri dish method. The BES population was selected 15 times with amitraz by LC60 values determined for each selected population. The resistant population was named as AMT 15. The resistance rate of this population after 15 selections was found 32.02 fold compared to the susceptible (GSS) population according to their LC50 values. Different synergists, piperonyl butoxide (PBO), triphenyl phosphate (TPP) and S-benzyl-O,O-diisopropyl phosphorothioate (IBP) + amitraz were applied to the AMT 15 resistant populations. PBO presented the highest synergistic effect with amitraz in AMT 15 population. The synergistic effects of the other synergists remained limited. Whether multi-resistance developed against some pesticides in the resistant AMT 15 population investigated. The highest multiresistance rate in AMT population was found against abamectin (8.34 fold) and propargite (6.37 fold). The only susceptibility in AMT 15 population was determined to bifentrin. The reciprocal crossing investigations revealed the resistance inheritance as incompletely dominant. The kinetic readings with microplate reader pointed significant increases in esterase (2.19 fold), gluthation - S - transferase (GST) (1.07 fold) and cytochrome P450 monooxygenase (P450) (29.24 fold), enzyme activities in AMT 15 population compared to the parental populations.