The purpose of this study was to investigate the influence of mandibular residual ridge shape on the masticatory ability in complete denture wearers.The subject group consisted of 199 complete denture wearers. The mandibular residual ridge of each subject was evaluated using a replica of the ridge which was obtained with heavy-body silicone impression material. The basal area of each replica was measured with a digitizer. The volume and the height of each replica were also calculated. The masticatory ability of each subject was evaluated using a-25-item food intake questionnaire method by authors. The masticatory score of each subject was calculated to represent the masticatory ability. Furthermore, all subjects were divided into three groups (S, M, L group) according to the value of the basal area.There were statistically significant correlations between the basal area of the residual ridge and the masticatory score (r = 0.366, p < 0.01), and also the volume of the residual ridge and the masticatory score (r = 0.314, p < 0.01). The basal area of the residual ridge, the volume of the residual ridge, and the masticatory score of the L group (29 persons) were statistically larger than those of the M group (136 persons) and the S group (34 persons) (p < 0.05), and those values in the M group were statistically larger than those of the S group (p < 0.05).It was confirmed that the basal area of denture foundation of the mandible had an influence on the masticatory ability in complete denture wearers.