The objective of this research is to study the optimum conditions for soil organic matter analysis. By using organic methods in soil analysis from the Department of Agriculture (Walkley Black modified acid-dichromate digestion, FeSO4 titration method) To test as follows: 1. Suitable soil weight for different types of soil such as clay, sand, loam (such soil is in Phetchaburi province) 2. Test the volume of the 1.0 N solution of potassium dichromate which provides the highest analysis efficiency 3. Test the volume of the concentrated sulfuric acid that provides the highest analysis efficiency, which found that 1. The suitable soil weight for analysis Organic matter For loam is 1 gram, 1.5 grams of sand and 0.5 grams of clay 2. The volume of the 1.0 N solution of potassium dichromate with the highest analysis efficiency is 10 milliliters. 3. The volume of concentrated sulfuric acid that provides the efficiency The maximum analysis is 20 milliliters.