Purpose: The deterioration of oral function has been getting much attention as “Oral frailty”. This study evaluated the change in tongue pressure, one of the objective items of oral frailty, to examine the relationship between body position and tongue pressure. Methods: This study was prospective, observational study in a single-center. The participants were categorized by Clinical Frailty Scale (CFS). Tongue pressure was measured in the following positions: dorsal, sitting, and sitting with plantar grounding. Differences in tongue pressure between CFS and between body positions were statistically analyzed. Results: A significant decrease in tongue pressure was demonstrated in CFS4 compared to CFS3. Furthermore, in CFS5 and CFS6, tongue pressure decreased in the sitting po-sition compared to that in the dorsal position and recovered to the dorsal level with plantar grounding. Conclusions: Tongue pressure decreased as the progression of frailty. It decreased by sitting, and this decrease was alleviated by plantar grounding.