A modification is proposed for Montgomery's procedure of the colorimetric deterurination of organic acids in the soil extraets. According to the equilibrium relationship in the chemical reactions, the soil extracts are dried on a boiling water bath before the esterification proceeded. As the extract is concentrated, the determination is free from the influence of aliquot volume and the organic acid concentration of the extracts. The factors including temperature, time and pH which affect the reactions in the procedars were tested. The recovery rate of acetic acid and butyric acid were 99% and 102% respectively. Acetic acid of several organic manure incubated under waterlogged condition for 10 days determined by the gas chromatography was 86% of that determined by the procedure suggested by the authors. This indicates that the results obtained by the modified method can better reflect the actual organic acid content in soil.