This study aimed to clarify the relationship between age and occlusal force in adults with natural dentition. A total of 385 adults (180 males and 205 females) with natural dentition participated in this study. Subjects were asked to perform maximum clenching for approximately 3 s, and the occlusal forces on both sides and habitual chewing side were calculated using a dental prescale. Regression analysis was performed by sex with occlusal forces on both sides and habitual chewing side as the dependent variable and age as the independent variable. In addition, all subjects were divided into three groups: young group (20-39 years), middle group (40-59 years), and old group (60 years and over), and the occlusal forces on both sides and habitual chewing side were compared among the three groups. The occlusal forces did not differ from 20 to 60 years old for both males and females, and the occlusal forces gradually decreased after 60 years old. The curve of the polynomial equation was the most suitable. The occlusal forces on both sides and the habitual chewing side were similar in the young and middle groups, and the values of the old group were significantly smaller than those of the other two groups. From these results, it was suggested that the occlusal force of adults with natural dentition does not differ from 20 to 60 years old and can be represented by a curve of a cubic polynomial, and it significantly decreases after 60 years old.