The purpose of this study was to evaluate the effect of factors influencing masticatory ability in adults. We examined adults from 18 to 86 years of age living in Yasuda Town, Niigata Prefecture. For subjective assessment of masticatory ability, we obtained data from 336 subjects about the food group in which subjects could chew all foods well, using the assessment chart of masticatory efficiency developed by Yamamoto. For objective assessment of masticatory ability, the amount of sugar elution from a piece of chewing gum was measured in 252 subjects who chewed the gum 100 times. In these assessments, subjects who ordinarily used dentures were tested without dentures.A stepwise multiple regression analysis was performed using 10 independent variables when explaining the food group in which subjects could chew all foods well, and using 11 independent variables when explaining the amounts of sugar elution.The results showed that the 5 statistically significant variables of the food group in which subjects could chew all foods well, listed in order of the values of the standardized partial regression coefficient were: ‘Number of missing teeth’, -0.671; ‘Using dentures ordinarily’, -0.182; ‘Knowlege of one's own general health’, -0.103; ‘Having jaw or oral pain excluding toothaches’, -0.081; and ‘Having loose teeth’, -0.061 (multiple correlation coefficient R=0.833, p<0.001). The 2 statistically significant variables of the amounts of sugar elution were: ‘Number of missing teeth’, -0.722; and ‘Amount of time required to chew a piece of gum 100 times’, 0.260 (multiple correlation coefficient R=0.668, p<0.001).It was concluded that the number of missing teeth was the factor with the highest standardized partial regression coefficient influencing masticatory ability both in subjective and objective assessments.