Type 2 diabetes mellitus (T2DM) and obesity often coexist and together contribute to left atrial (LA) functional abnormalities. However, little is known about the impact of body mass index (BMI) on LA strains measured using cardiac magnetic resonance feature tracking (MR-FT).To investigate the additive effect of BMI on LA functional remodeling using MR-FT as well as to explore abnormal atrioventricular interaction in T2DM patients.Retrospective.One hundred and fifty-nine T2DM patients (53, 34, and 72 normal-weight, overweight, and obese individuals) and 105 non-diabetic controls (46, 32, and 27 normal-weight, overweight, and obese individuals).3.0 T/balanced steady-state free precession.LA reservoir strain (εs ), conduit strain (εe ), and active strain (εa ) and their corresponding strain rates (SRs, SRe, SRa) were measured together with left ventricular (LV) radial, circumferential, and longitudinal peak strain, peak systolic strain rate, and peak diastolic strain rate.Student's t-test or Mann-Whitney U test, one-way ANOVA, univariate and multivariate linear regression. A P value <0.05 was considered statistically significant.Compared to controls in the same BMI category, T2DM patients had significantly decreased reservoir and conduit function, while pump function was not significantly different (εa and SRa: P = 0.757 and 0.583 for normal-weight, P = 0.171 and 0.426 for overweight, P = 0.067 and 0.330 for obese). LA strains were significantly correlated with BMI (r = -0.346 for εs , -0.345 for εe ) in T2DM patients. Multivariable linear regression analysis indicated that BMI was independently associated with LA εs and εe , LV global longitudinal strain was independently associated with LA εs and εa , and LV circumferential peak diastolic strain rate was independently associated with LA εe .These findings suggest that the coexistence of increased body weight and T2DM patients can exacerbate the impairment of LA strains and indicate abnormal atrioventricular interactions.3 TECHNICAL EFFICACY: Stage 3.© 2021 International Society for Magnetic Resonance in Medicine.