Purpose: The deterioration of oral function has received much attention, also being referred to 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 a prospective, observational study conducted in a single center. The participants were categorized by their Clinical Frailty Scale (CFS) scores. 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 position compared to that in the dorsal position, and tongue pressure recovered to the dorsal level with plantar grounding. Conclusions: Tongue pressure decreased with the progression of frailty. It was decreased by sitting, and this decrease was alleviated by plantar grounding.