BACKGROUND For complete denture wearers the tongue plays an important role in the retention and stability of dentures and has a great influence on masticatory function. OBJECTIVE The purpose of this study was to elucidate the relationship between tongue motor behavior and masticatory function. METHODS Thirty healthy, normal adult dentates, 10 normal elderly dentates, and 20 complete denture wearers whose dentures were constructed by the same methods and materials were selected. Tongue motor skills were examined by an ultrasound system and masticatory performance was evaluated by the sieving method. RESULTS The tongue motor skills of elderly dentates and complete denture wearers were statistically lower compared with those of adult dentates (p < 0.05, Duncan test). Tongue motor skills of complete denture wearers were statistically correlated with age (p < 0.01). Masticatory performance was statistically lower in relation to age in complete denture wearers (p < 0.01). The correlation coefficient was 0.74 between tongue motor skill and masticatory performance in complete denture wearers, which was statistically significant (p < 0.01). CONCLUSIONS Age-related decreases in tongue motor skills and masticatory performance were demonstrated by ultrasound observations and sieving methods.