This paper repotrs strain and frequency dependencies of dynamic viscoelasticity of commercial plain yoghurts and trial foods for swallowing disorders. We prepared four test samples adjusting hardness to a level similar to that of commercial plain yoghurts. Guar gum and modified starch were used as ingredients for preparation of two samples, respectively. Commercial plain yoghurts and modified starch samples exhibited viscoelastic behaviors strongly dependent on shear, while they behaved as nearly elastic material in the linear viscoelastic region. These properties are shown to be consistent to the swallowing mechanism to which well organized cooperative motions of several organs are related. Viscoelastic properties of guar gum samples were found to be quite different from those of commercial plain yoghurts, which suggests that modified starch is a better ingredient than guar gum for preparation of test samples and for detailed research on swallowing disorders.