Objective: To investigate the effect of long-term water exercise on gait parameters in the elderly post stroke patients. Design: One group pretest-posttest design. Methods: Twenty elderly post stroke patients (age: 56.5±10.1 years, height: 168.6±5.8 cm, body mass: 69.3±6.9 kg, handicapped level: 2.5±0.8) participated in this study. Participants took part in gait training of 1 hour per day, three days per week, for three months. Participants’ gaits were analyzed to find the effect of 3 months water exercise by a 3-D motion analysis with 8 infrared camera and 1 force plate (sampling frequency: 100 and 1,000 Hz, respectively). A paired t-test was used to find the significance with significant level as 0.05. Results: Gait velocity, step length & step width significantly increased, and asymmetric index for gait parameters significantly decreased after the water exercise (p＜0.05). Conclusions: The water exercise effectively affect on patients’ gait ability and electromyography analysis will be needed further study.