The Motricity Index (MI) can predict motor function after rehabilitation, but its minimal clinically important difference (MCID) has not been established. The primary study aim was to estimate the MCID value of the MI arm score. Between 2017 and 2018, 173 participants hospitalized with confirmed ischemic stroke were recruited into an observational rehabilitation study. Participants with motor weakness as measured by the Fugl-Meyer upper-extremity (FM-UE) and MI with complete baseline and follow-up assessments at 3 months were included in this analysis. The longitudinal recovery of the MI arm score was anchored to having a poor outcome based on the FM-UE recovery (