Pesticides are playing a main role in modern agriculture and ranching. Acaricides are used in very large quantities in different c ountries. Environmental concerns have raised the necessity of control and detection of these compounds. In this study, hollow fiber-based liquid- liquid microextraction (HF-LPME) combined with gas chromatography- electrone capture detection (GC-ECD) was applied for extraction and determination of four acaricides (dichlorvos, chlorpyrifos-methyl, chlorpyrifos and bromopropylate) in biological and water samples. Parameters affecting the sample enrichment step, such as extracting solvent, salt addition, stirring rate, extraction time and temperature were studied and optimized. The analytes were extracted from a 3-mL sample solution by 3-µL hexyl acetate using a 9-mm hollow-fiber. A 25-?L HPLC-GC syringe with exchangable needles was used for fixing the hollow-fiber and injecting to GC. Under the optimized conditions (hexyl acetate as organic solvent, stirring rate of 1000 rpm, 20 min extraction time, no salt addition, at 45 o C), the limits of detection were ranged from 0.7 to 3.6 ng/L. The between-day and within-day relative standard deviations were in the range of 3.9-11.3 % and 1.4-4.5 %, respectively. The method provided 71–201 fold preconcentration of target analytes. Correlation coefficients were ranged from 0.991 to 0.999. Real samples (River water, cow and human urine) spiked with acaricides were examined using this method. Good linear ranges and precisions (RSDs lower than 7 % for many of compounds) were obtained. Recoveries were ranged from 88 to 116 %.