Background Previous studies have shown that diffusion‐weighted imaging (DWI) is sensitive to myocardial fibrosis in ischemic and nonischemic cardiomyopathy. Purpose To explore the prognostic value of apparent diffusion coefficient (ADC) for detecting myocardial fibrosis and its relationship to the contractile function in hypertrophic cardiomyopathy (HCM). Study Type Prospective. Population A total of 45 HCM patients and 20 controls. Field Strength/Sequence 3.0T cardiac MRI. The cardiac MR sequences included cine, T1 mapping, and DWI. Assessment According to the presence of late gadolinium enhancement (LGE) and the extracellular volume (ECV) values (+2 SD of control subjects), respectively, reader W and reader J assessed the value of ADC of each segment for detecting myocardial fibrosis and its relationship to impaired contractile function in HCM patients. Statistical Tests Independent sample t‐test, Pearson analysis, and intraclass correlation (ICC). Results The value of ECV was 23.6 ± 3.0% for control. ECV ≥ 29.6% and ECV < 29.6% groups were classified. ADC values in the ECV ≥ 29.6% group were significantly increased compared to the ECV < 29.6% group, (2.41 ± 0.23 μm2/ms vs. 2.03 ± 0.16 μm2/ms, P < 0.005). Compared to the LGE – group, ECV (32.1 ± 2.3% vs. 29.0 ± 2.8%, P < 0.005) and ADC (2.60 ± 0.18 μm2/ms vs. 2.10 ± 0.07 μm2/ms, P < 0.005) values were significantly increased in the LGE + group. ADC values were linearly associated with ECV values (R2 = 0.65) in HCM patients. ADC values were linearly associated with circumferential and longitudinal strain (R2 = 0.60, R2 = 0.46), as well as circumferential, longitudinal, and radial strain rate (R2 = 0.13, R2 = 0.25, R2 = 0.17, respectively). Data Conclusion Contractile dysfunction in HCM is predominantly associated with ADC, which is a feasible alternative to ECV and LGE for detecting myocardial fibrosis. Level of Evidence: 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;48:1139–1146.