In this study, we made the first investigation on abnormal pattern of dynamic functional connection density (dFCD) in ALS. We gathered resting state functional magnetic resonance imaging (fMRI) data from 50 patients with ALS and 55 healthy controls (HC). dFCD was analyzed by sliding window correlation method; and the standard deviation of dFCD across the sliding window was calculated voxel-wisely to quantify dFCD variability. Our study has found abnormal dFCD variability in ALS. The indices of dFCD variability showed moderate discrimination power between two groups, suggesting its potential serving as the diagnostic biomarker for ALS.