Purpose: The purpose of this study was to investigate the influence of mandibular residual ridge shape on the masticatory ability in complete denture wearers.<br>Methods: 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.<br>Results: 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).<br>Conclusion: It was confirmed that the basal area of denture foundation of the mandible had an influence on the masticatory ability in complete denture wearers.