[Abstract] Objective: To comparatively explore the value of left ventricular end-diastolic maximal wall thickness (MWT) and anatomical parameters of left ventricular outflow tract (LVOT) for evaluating myocardial fibrosis in hypertrophic cardiomyopathy (HCM) by cardiac magnetic resonance (CMR) and propose a prediction model. Methods: Seventy-seven HCM patients who underwent CMR examination were retrospectively analyzed. CMR data included partial anterior mitral leaflet length and total anterior mitral leaflet length. During end-diastole and end-systole, the diameter of LVOT and the thickness of basal anteroseptal were measured. Additionally, left ventricular end-diastolic MWT was collected and the percentage of late gadolinium enhancement (LGE%) was analyzed. LGE% was used to assess myocardial fibrosis. Seventy percent of the samples selected randomly by statistical software were assigned to the derivation cohort for establishing a prediction model of LGE% through univariable and multivariable analysis. The remaining thirty percent of the samples served as the internal validation cohort, and parameters of echocardiogram of all patients were used for external validation to assess the accuracy of the prediction model. Receiver operating characteristic curves were plotted, and the predictive efficacy of the prediction model was determined by calculating the area under the curve. The sensitivity and specificity of the prediction model were also evaluated. Results: In the derivation cohort, multivariable analysis indicated that MWT was an independent predictor of LGE% with the linear equation LGE% = -10.009 + 0.832 × MWT (r = 0.466, P < 0.001), while no anatomical parameters of LVOT were correlated with LGE%. In the validation cohort, there was no statistical difference between MWT measured by echocardiogram and MWT measured by CMR. Additionally, the predicted values from both internal and external validations showed no statistical difference from LGE%. The accuracy of predicting LGE%≥15% were 82.6% with a cutoff of 30mm for MWT measured by CMR and 81.7% with a cutoff of 25mm for MWT measured by echocardiogram respectively. Conclusion: When evaluating myocardial fibrosis in HCM, MWT has more predictive value than anatomical parameters of LVOT.