Background and Objectives: Quantification of severity of mitral regurgitation (MR) is a major issue in management of the disease, and various methods have been proposed for this purpose. We evaluated the efficacy and feasibility of a new method for quantification of MR grade associated with microbubble washout time. Methods: Twenty-nine patients with various grades of MR were enrolled prospectively. Fourteen of them had mild MR, 7 moderate MR, and 8 severe MR on Doppler examination. Contrast echocardiography(CE) was performed with an intravenous bolus injection of perfluorocarbon exposed sonication dextrose albumin (PESDA). ECG-triggered end-systolic images were obtained digitally on apical 4-chamber view, beginning from the frame where the microbubbles first appeared in the right atrium and ending when the left atrium (LA) was void of contrast. Videodensity-time curves in the LA were analyzed offline with gamma-variate fitting. The correlation between parameters of videointensity-time curve and echocardiographic quantitative parameters of MR such as regurgitant jet area(RJA), vena contracta(VC), proximal isovelocity surface area(PISA) radius, effective regurgitant orifice area(EROA), and regurgitant volume(REV) were investigated. Results: The time to peak intensity (TPI), time to 75% washout point(TWP75), and area under the curve (AUC) of the videointensity-time curves of LA showed significant positive correlations with semi-quantitative color Doppler MR grade (r=0.71, 0.69, and 0.62, respectively, p<0.01). These parameters also showed significant correlations with other echocardiographic parameters of MR grade such as PISA radius(r=0.69, 0.69, and 0.62, respectively, p< 0.01), EROA(r=0.66, 0.66, and 0.53, respectively, p< 0.01), and REV(r=0.70, 0.69, and 0.57, respectively, p<0.01), respectively. Conclusion: Quantification of MR with microbubble washout time is a new, simple, and safe method which shows good correlations with other echocardiographic parameters such as PISA radius, EROA, and REV. Our new method for MR grading by CE will be complementary to accurate grading of MR in clinical practice, especially in the presence of eccentric or multiple regurgitant jets.