Acrinathrin [(S)-a-cyano-3-phenoxybenzyl (Z)-(1R,3S)-2,2-dimethyl-3-[2-(2,2,2-trifluoro-l-trifluoromethyl-ethoxycarbonyl)vinyl]cyclopropanecarboxylate] is an acaricide insecticide pyrethroid acting through contact and ingestion by such insects as phytophagous mites on citrus, cotton, fruit, hops, ornamentals, soyabeans, tobacco, vegetables, vines and greenhouse crops. Its half life in water is longer than other pesticides even under photolysis by natural sunlight. Acrinathrin is manufactured by Roussel Uclaf under the tradename of Rufast (15% acrinathrin w/v). A method for the determination of acrinathrin residue in vegetables by gas chromatography was proposed by Fernandez-Alba using electron capture detector (GC-ECD), with a determination limit of 0.001 mg kg-1. Here, we propose a method for the determination of acrinathrin in ground and sea water based in a hexane micro liquid-liquid extraction, a technique which has also been applied to the detection of some pyretroids and endosulfans in water.