A study was undertaken to investigate the persistence of 2,4-D and MCPP in two different Suweon soils under field conditions. MCPP was extracted from soil with aqueous calcium hydroxide solution and then derivatized to pentafluorobenzyl ester to enhance the electron capture sensitivity. Total recovery of MCPP from soil was 85.6% and the detection limit for 20g sample was 0.02 ppm. Ethyl ester of 2,4-D applied to soil was rapidly hydrolysed to 2,4-D with the half-life of less than 1 day. Half-life of total 2,4-D ethyl ester, including 2,4-D, incorporated into soils at a rate of 0.045 ㎏ a.i./10a was $4{sim}7$ days and that of under laboratory conditions was $7{sim}8$ days. Half-life of MCPP applied at a rate of 0.25㎏ a.i./10a under field conditions was $9{sim}12$ days and that of under laboratory conditions was $12{sim}23$ days.