This study evaluated the impact of ventricular rate (VR) in atrial fibrillation (AF) patients with oscillometric BP measurements. This study included 138 patients with AF and 112 patients with sinus rhythm (SR) who underwent coronary angiography. Left arm BP was measured three times with an oscillometric device, and the average was recorded as the final oscillometric value. At the same time, the average of three intra-aortic BP readings was used as invasive values. Delta BP was the difference between intra-aortic and oscillometric BP. Meanwhile, the BP percentage difference (PD-BP) was calculated with the following formula: PD-BP = (delta BP/intra-aortic BP) × 100%. Based on the VR, four subgroups of AF and SR patients, <80, 80-99, 100-120, and >120 bpm, were created, and the mean PD-BP for both systolic blood pressure (SBP) and diastolic blood pressure (DBP) was significantly higher in the AF group than in the SR group. Moreover, the mean PD-SBP values gradually increased as VR increased in both groups. More importantly, the difference in PD-SBP between the AF and SR groups increased as VR increased: when VR was <80 bpm, the levels were similar (-2.0 ± 3.5 vs. -1.4 ± 2.7 mm Hg, NS), but these values in AF patients were significantly higher when VR was 80-99 bpm (-3.7 ± 5.0 vs. -1.8 ± 2.3 mm Hg, p < 0.05), 100-120 bpm (-6.1 ± 4.3 vs. -2.3 ± 1.9 mm Hg, p < 0.05) and >120 bpm (-7.8 ± 4.9 vs. -2.9 ± 1.7 mm Hg, p < 0.05). The accuracy of oscillometric BP measurements are dependent on the ventricular rate in AF patients even after three measurements, and a higher ventricular rate may result in larger underestimations of oscillometric BP.