The present study used semi-liquid foods, prepared in three different levels of hardness with the use of commercial thickening agents (containing xanthan gum, guar gum, or processed starch as the main substance for thickening), as samples to examine the relation between the physical properties of those food samples and the electromyography (EMG) of human beings during swallowing. The EMG during swallowing was obtained through measurement of EMG from supra-hyoid musculatures during swallowing. The flow behavior and the frequency dependence of dynamic viscosity, obtained through measurements of physical properties, demonstrated that the xanthan gum sample and processed starch sample have weak gel structures, and that the gel structure was particularly strong for xanthan gum sample. In contrast, the guar gum sample was found to have a sol-like structure. For the xanthan gum sample which has a gel structure in the solution, the harder the sample, the larger the EMG during swallowing tended to be. In the case of samples with hardness level of 8×10²N/m², which is the hardest sample used in the present study, the EMG during swallowing for xanthan gum sample was found to be significantly larger compared with that of the sol-structured guar gum sample. These findings suggest that, for xanthan gum sample, the harder the sample, the more swallowing efforts are being made by human beings when conveying the sample bolus from the oral cavity to the pharynx. It can also be assumed that, among samples at a hardness level of 8×10²N/m², which requires more swallowing efforts compared with samples of other hardness levels used in the present study, the EMG during swallowing for guar gum sample that demonstrates sol-like structure when the sample bolus is being conveyed from the oral cavity to the pharynx, was significantly smaller compared with that of the xanthan gum sample. The outcome of the present study suggest that, for semi-liquid foods prepared with the use of commercial thickening substances as swallow-support agents, the hardness level of the semi-liquid food can exert different influences on the EMG during swallowing, depending on the main ingredient used as thickening substance.