Background: Stroke recovery is a long and complex process. Successful stroke recovery seems to be strongly associated with patients’ high motivation and committed participation. Patients’ motivation is a key determinant of successful rehabilitation outcomes, but it is difficult in defining and measuring. Patients’ participation is defined as the degree or extent to which subjects take part in rehabilitation activities and can be measured by observable behavior. Objects: The purpose of this study was to investigate the impact of patients’ level of participation in rehabilitation on functional outcomes in patients with stroke. Methods: Forty post-stroke inpatients participated in this study. The level of rehabilitation participation was measured by the Hopkins Rehabilitation Engagement Rating Scale (HRERS). Other measures used for the evaluation were the Rivermead Mobility Index (RMI) and Korean version of the Modified Barthel Index (K-MBI). Overall measurements were made at early intervention and late intervention. Spearman correlation and multiple regression were used to measure the relationships between HRERS, RMI, and K-MBI. Results: The correlation found between HRERS total scores at early intervention and RMI total scores of late intervention was above moderate (r = 0.607, p < 0.01). RMI total scores at early intervention (p < 0.000), HRERS total scores at early intervention (p < 0.001), and disease duration (p < 0.003) were significant predictors of RMI total scores at late intervention. Conclusion: The level of participation at early intervention was associated with improvement in mobility. The level of mobility at early intervention, disease duration, and patients’ participation at early intervention were important determinants of functional outcome. These findings suggest that patients’ participation should be encouraged in order to achieve successful stroke recovery.