The government policy is to increase grain protein of soybean for soy food products. Then soybean variety improvement to increase grain protein content was initiated. The seed of three soybean varieties namely Chiang Mai 60, SSRSN19-35-4 and EHP275 were irradiated with 200 gray. Pedigree method of selection was used at Nakhon Ratchasima FCRC and grain protein of the mutants was analyzed in laboratory at the Department of Agriculture, Bangkok [6]. A number of 32 mutant lines were selected. The result of a preliminary trial at Nakhorn Ratchasima FCRC in 2007 showed that the lines gave average grain protein of 0.8, 2.0 and 1.0% higher than the original parents of 41.8, 40.3 and 41.9%, respectively [7]. Then it is possible to enhance grain protein percentage with similar or higher yield in the soybean varieties using induced mutation. The promising mutant lines will be further tested for their protein yield in farmer fields.