The liquefying properties of starch were found to be affected by defatting. Potato starch which is known to contain little fat was given a bad influence by heat during defatting. On the contrary corn starch which contains much more fat and has less susceptibility to heat was given a good influence. The liquefying properties of starch, into which saturated monobasic fatty acids (from butyric to stearic) were incorporated, were investigated. The lower fatty acids which have smaller carbon number than capric acid had little influence, but the higher fatty acids than lauric acid were considered to form, with starch molecules, the compound incapable of being decomposed by liquefying enzyme, and gave an unfavorable influence on liquefaction of starch.