This study aimed to evaluate the utility of dual-source computed tomography (DSCT) for quantification of the mitral valve area (MVA) in patients with atrial fibrillation (AF) and mitral stenosis (MS) and to compare the results of DSCT with those of cardiovascular magnetic resonance (CMR) and transthoracic echocardiography (TTE). One hundred-two patients with AF and MS who had undergone electrocardiography-gated DSCT, TTE and CMR prior to operation were retrospectively enrolled. The MVA was planimetrically determined by DSCT, CMR, and TTE, as well as by Doppler TTE using the pressure half-time method (TTE-PHT). Agreement, relationship between measurements, and the highest accuracy were evaluated using Bland-Altman, Pearson correlation, and receiver operating characteristic analyses. The MVA on DSCT (mean, 1.27 ± 0.27 cm(2)) was significantly larger than that on CMR (1.15 ± 0.28 cm(2), P < 0.05), TTE-planimetry and TTE-PHT (1.16 ± 0.28 and 1.07 ± 0.30 cm(2), respectively; P < 0.05). TTE-planimetry had better correlation with planimetry on DSCT and CMR (r = 0.65 and 0.67, respectively; P < 0.05) than TTE-PHT (r = 0.51 and 0.55, respectively; P < 0.05). Using an MVA of 1.0 cm(2) on TTE-planimetry and TTE-PHT as the reference, the optimal thresholds for detecting severe MS on DSCT was 1.19 cm(2). The planimetry of the MVA measured by DSCT may be a reliable, alternative method for the quantification of MS in patients with AF.