OBJECTIVES: To date, controlled clinical trials evaluating the efficacy of underwater exercise in improving the lower-extremity function and quality of life (QOL) in post-stroke patients have yet to be conducted. The purpose of the present study was to determine whether repeated underwater exercise enhances the therapeutic effect of conventional therapy for post-stroke patients. DESIGN: This was a pilot controlled clinical trial. SETTING: The study took place in a research facility attached to a rehabilitation hospital. PATIENTS: This prospective trial included 120 consecutive post-stroke inpatients with hemiplegic lower limbs (Brunnstrom stage 3-6). Patients were assigned to either an experimental or a control group. Patients in the experimental group received both repeated underwater exercise and conventional rehabilitation therapy. INTERVENTIONS: The underwater exercise consisted of 30-min training sessions in a pool with a water temperature of 30-31°C in which patients followed the directions and movements of trained staff. Training sessions were conducted once a day on 2 days of the week for a total of 24 times. Patients in the control group received only the conventional therapy. OUTCOME MEASURES: The 10-Minute Walk Test (10MWT), the Modified Ashworth Scale, and the 36-Item Short Form Health Survey were the outcome measures used. Lower-extremity function and QOL were assessed before and upon completion of the 12-week program. RESULTS: Improvements in 10MWT results and spasticity parameters were greater in the experimental group than they were in the control group (p < 0.01). Significant differences between the groups were observed in magnitudes of changes of all QOL parameters (p < 0.01). CONCLUSIONS: Combining conventional therapy with repeated underwater exercise may improve both lower-extremity function and QOL in post-stroke patients.