Invertase activity of the soil is generally estimated from the concentration of the invert sugar through by drolysis of sucrose by the invertase. Owing to the presence of soil organic matter, the coloration of soil solution usually introduces interference is polariscopic, colorimetric, and ordinary titration methods. Present investigation suggests the adoption of Tryller's potentiometric titration method provided with a magic eye for determining invertase activity. Determinations were made on agricultural soils grown wheat, sweet potatoes and onion. Results showed that activity of invertase varies with the kinds of chemical fertilizers applied and also with the depth of soils.