The purpose of this study is to clarify the relation among the viscosity values of semi-solid diets and the electrical mechanism of gastric motility. Firstly, a measurement procedure suitable for stomach physiology was proposed. A new measurement procedure lessened the psychological and physiological burdens of the subjects, and controlled the cycle of gastric activity of the subjects. And the dispersion of data for subjects was decreased by this new method, in which the measurements were started after 4 hours fasting. Secondly, we prepared five grades of viscosities of fluid to semi-solid diets from low to high viscosity (30 mPa·s ∼ 20000 mPa·s) mixed by five different amounts of two kinds of thickening agents. The measurements were performed for 8 healthy volunteer subjects. By evaluating DPr (Dominant Power ratio: Ratio of post/pre-prandial DP values), a significant increment by ingestion of high viscosity semi-solid diets was confirmed in both kinds of thickening agents. DFD (Dominant Frequency Dispersion) was significantly decreased in both high viscosity semi-solid diets. Thus, these results suggested that gastric activity was physiologically stimulated and the cycle of gastric activity became stable by ingestion of high viscosity diets. The results showed that an electrophysiological phenomenon in the evaluation of electrogastrography (EGG) is affected by the viscosity of diets, and also suggested that the difference in the shear rate dependence of diets was not really significant to the electrical behavior of gastric motility.