This study aimed to determine the sensitivity levels of Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) populations collected from the apple orchards in Isparta in 2011 to etoxazole, hexythiazox and spirodiclofen by using bioassay methods. LC50 values of N. californicus populations were determined by using a spray tower with the leaf disk method. According to LC50 values, compared susceptible populations, resistance of Atabey-1, Atabey-2, Agilkoy-1, Agilkoy-2, Gonen and Yalvac populations collected from the orchard in 2011 is determined to be 10.14, 11.34, 11.75, 14.41, 9.85 and 9.66 fold to etoxazole; to be 6.35, 3.96, 9.33, 8.35, 7.34 and 9.79 fold to hexythiazox; and to be 4.61, 4.36, 5.86, 4.82, 4.10 and 7.08 fold, respectively. Moreover, the effect of the PBO, IBP and DEM synergists on pesticides was examined. Enzymes of S-transferase (GST), monooxygenases (P450) and acetylcholinesterase (AChE) in the popluations were determined by using the kinetic method; and the enzyme of esterase was determined by using the electrophoresis and kinetic methods. The determined enzyme activity ranges of esterase, glutathion S-transferaz (GST), monooxygenases (P450) ye asetilkolinesteraz (AChE) were between from 7.130 to 11.788, from 2.07 to 3.47, from 0.0223 to 0.0695 and from 0.0211 to 0.0243 mOD/min/mg proteins, respectively.