Abstract: The method of determination of medroxyprogesterone acetate residue in aquatic product by liquid chromatography with electrospray ionisation tandem mass spectrometric detection is described. The compound was extracted with ethyl acetate and evaporated to dryness, dissolved with acetonitrile and defatted with n-hexane, followed purified with neutral alumina solid- phase extraction cartridges. Sample was chromatographed using an acetonitrile 0.1% formic acid (7:3,v/v) mobile phase on a Symmetry Shield RP18 column. Analyte determination was performed by ESI-MS-MS in the multiple reaction monitoring (MRM) mode. The method was accurate and reproducible, at a spiking level from 0.1 μg/kg to 20 μg/kg, recovery ranged from 92% to 106%, coefficient of variation ranged from 3% to 7%, the limit of detection was 0.03 μg/kg and the limit of quantitation was 0.1 μg/kg.