To determine the influence of right bundle branch block (RBBB) on right ventricular (RV) size and function, we investigated the association between complete RBBB (CRBBB) and RV volume, function, and dyssynchrony by three-dimensional echocardiography. In this retrospective, cross-sectional study, 103 consecutive patients with adequate three-dimensional echocardiographic images were divided into the CRBBB, middle-range QRS, and narrow QRS group. RV volumetric and functional data were compared between the three groups. Among the 103 patients (44.8 ± 18.7 years, 50 men), the CRBBB group comprised 26 (25%) patients and the middle-range QRS group comprised 48 (47%). The CRBBB group showed a significant contraction delay in the RV inlet free wall and outflow tract; larger RV end-diastolic and systolic volume index (RV-EDVI, RV-ESVI); and lower RV systolic function. On dividing the CRBBB patients into two (with or without mechanical dyssynchrony), those with RV dyssynchrony showed larger RV-EDVI (121 ± 45 vs. 85 ± 25 mL/m², P = 0.019) and RV-ESVI (93 ± 42 vs. 56 ± 20 mL/m², P = 0.009) and smaller RV ejection fraction (24 ± 11 and 34 ± 11%, P = 0.026) than those without RV dyssynchrony. RV dyssynchrony in CRBBB patients might have an adverse effect on RV volume and function. Three-dimensional speckle-tracking echocardiography could provide additional and beneficial data during assessment of RV dyssynchrony.