Abstract. Liquid phase oxidation of n-pentane without oxidate water-acid layer withdrawal from the oxidation zone, with oxidate water-acid layer withdrawal from the oxidation zone and by stages oxidation of the n-pentane with the oxidate water-acid layer withdrawal from the oxidation zone was studied at the temperature 165o C and pressure 5.06 MPa. It has been determined that total selectivity of formation of lower carboxylic acids increases 1.46 times the size, propionic acid 2.28 times the size and formic acid 1.2 times the size at by stages liquid phase oxidation of the n-pentane with the oxidate water-acid layer withdrawal from the oxidation zone comparing with ordinary oxidation of n-pentane. A new technological line of formic, acetic and propionic acids obtaining by the by stages liquid phase oxidation of light hydrocarbon fractions with the oxidate water-acid layer withdrawal from the oxidation zone is offered.