Stroke, which means nerve injury, causes diverse kinds of impairment according to the aspects or the extent of the injury. Among these impairments, gait impairment, which influences the quality of life of stroke patients, is regarded to be a very important factor. Gait is an exercise process related to multiple factors such as gender, age, muscular strength, and balance. Above all, stroke patients' loss of balance makes it difficult for themselves to take a quick and proper posture. Asymmetric posture of stroke patients in walking distributes body weight toward legs unequally, specifically, more body weight toward a less affected leg. The purpose of this study is to apply hydrotherapy efficiently to rehabilitation treatment of stroke patients through research on the change of distribution of body weight on both legs in underwater exercise for balance. This study was executed on 12 patients who were diagnosed to be hemiplegia and received treatment in hospital. The patients were classified by experimental group(5) and control group(7). Experimental group received both hydrotherapy and conventional physical therapy. But control group received only conventional physical therapy. On experiment, peak pressure and total pressure were generated by weight of both legs in walking were evaluated through F-Scan. The evaluation data were analyzed through repeated measurement ANOVA. In case of experimental group, the average peak pressure 5.85(4.37)kg before experiment was decreased to the extent of 1.99(2.48)kg after experiment. In case of control group which was not treated by hydrotherapy, the average peak pressure 7.71(9.39)kg before experiment was decreased to the extent of 4.01(4.37)kg after experiment. But the result of repeated measurement ANOVA on before and after experiment indicated that there occurred no significant statistical difference, namely p<0.05, between experimental group and control group. In case of experimental group, the average total pressure 108.94(72.62)kg before experiment decreased to the extent of 24.18(15.55)kg after experiment. In case of control group, on the contrary, the average total pressure 30.58(24.19)kg before experiment increased to the extent of 59.05(4.37) kg after experiment. The result of repeated measurement ANOVA on before and after experiment indicated that there occurred no significant statistical difference, namely p<0.05. Although the difference in peak pressure of both legs in walking was evaluated through repeated measurement ANOVA there occurred no significant statistical difference and the average of both experimental group and control group decreased, while that symmetry of both legs increased. Considering that the change of the average of experimental group was bigger than that of control group, the effectiveness of hydrotherapy was demonstrated to be useful, suggesting more proliferated researches. In addition, what the difference in total pressure of both legs in walking was evaluated through repeated measurement ANOVA indicated that there occurred a significant statistical difference, suggesting that hydrotherapy can be effective in decreasing the difference of total pressure of hemiplegia patients in walking. Though the difference of peak pressure in walking showed no significant statistical difference between experimental group and control group, the decrease of the average of experimental group was bigger than that of control group, indicating the effectiveness of hydrotherapy. In addition, the difference of total pressure showed a significant statistical difference between experimental group and control group, indicating that hydrotherapy can be effective in increasing of symmetry of hemiplegia patients in walking.