The purpose of this study was to investigate the effect of aqua exercise on women 50 years of age or older with knee degenerative arthritis, and then examining the therapeutic value of aqua exercise in degenerative arthritis of the knee. The subjects of the study were 115 residents 50 years of age or older who had been diagnosed as degenerative arthritis of the knee by doctors from medical institutions and applied for the aqua exercise program in the Public Health Care Center in Suseong-gu in 2006 and 2007. Experiments were conducted to all the subjects with the application of the 8-week aqua exercise program (2 times a week, 50 minutes a time), designed in the study, and the differences before and after the aqua exercise were compared through questionnaires for measuring the state of the body such as the knee extension angles, weight, body fat, and abdominal obesity. The data was analyzed by t-test and the Wilcoxon method through SPSS 14.0 and the statistical significance level ${alpha}$ was set at 0.05 and 0.01. The results of the study are as the following. First, In comparison of before and after the aqua exercise, there was improvement in the extension angle of the right knee(p<0.01), while there was some improvement in the extension angle of the left knee, it was not significant. Second, In comparison of before and after the aqua exercise there were statistically significant differences in weight(p<0.05), body fat ratio, and abdominal obesity(p<0.01). The results of this study showed that the aqua exercise program to female patients with knee degenerative arthritis significantly increased the extension angle of the knee. Therefore it is thought that aqua exercise is an effective meditating method to improve their symptoms of female patients 50 years of age or older