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BackgroundVariable flip angle (VFA) and modified Look–Locker inversion recovery (MOLLI) are frequently used for noninvasive evaluation of renal interstitial fibrosis (IF) in chronic kidney disease (CKD). However, controversy remains over which method is preferred.PurposeTo compare the diagnostic efficacy of VFA and MOLLI for T1 mapping in evaluating renal IF.Study TypeProspective.SubjectsFifty‐one participants with CKD (CKD stage 1–5, 35 males) and 18 healthy volunteers (eight males).Field Strength/Sequence3.0 T, three‐dimensional gradient echo sequence for B1+ VFA, and two‐dimensional gradient echo sequence for MOLLI.AssessmentImage quality was assessed on a five‐point scale. Cortex and medulla T1 values (cT1 and mT1), corticomedullary T1 value difference (ΔT1, medulla − cortex), and corticomedullary T1 value ratio (ratio T1, cortex:medulla) were compared between VFA and MOLLI as well as between IF grade (0–4) based on biopsy.Statistical TestsIntraclass correlation coefficient, Bland–Altman analysis, analysis of variance, Kruskal–Wallis test, correlation analysis, and receiver operating characteristics analysis with the area under the curve (AUC). P‐value <0.05 was considered significant.ResultsMOLLI provided significantly better image quality compared to VFA. cT1 and mT1 values significantly differed between VFA and MOLLI (cT1‐VFA: 1771.4 ± 139.4 msec vs. cT1‐MOLLI: 1729.9 ± 132.1 msec; mT1‐VFA: 2076.0 [interquartile range (IQR): 2045.9–2129.9] msec vs. mT1‐MOLLI: 2039.2 [IQR: 1997.8–2071.6] msec). ΔT1 and ratio T1 values were not different between VFA and MOLLI (ΔT1: 300.8 ± 71.4 vs. 306.0 ± 78.4, respectively, P = 0.33 and ratio T1: 0.85 ± 0.038 vs. 0.85 ± 0.041, respectively, P = 0.064). No difference was observed between T1 variables and T1 mapping methods in diagnosing IF.Data ConclusionΔT1 and ratio T1 were not different between VFA and MOLLI. Both VFA and MOLLI are effective for noninvasive assessment of renal IF.Level of Evidence2Technical EfficacyStage 2