A study has been conducted to ascertain persistency of p-chlorophenoxy acetic acid (CPA), a plant growth substance, in soil. CPA was extracted from soil and then converted to a glc (ECD) sensitive derivative, 2-chloroethyl p-chlorophenoxy acetate (CPA ester) with BCI₃ as catalyst. Total recovery of CPA including the chemical conversion was 49.4% and detection limit of CPA in soil, a minimum concentration of the compound which can be identified on chromatogram, was 0.03 ppm. Half life of CPA in clay loam under field conditions was 20 days and that of CPA under laboratory condition was 27.4 days respectively.