This study was to investigate the effects(pain, discomfort, and range of motion) of heat therapy according to the application time among the elderly with osteoarthritis. Study participants were 27 elderly women, who were diagnosed as osteoarthritis, suffered from it for more than 6 months, and who were staying at a nursing home in Busan. The independent variable was heat therapy, which was applied for 20minutes, one time per week according to 3 timetable(before waking up, while in daily living, before going to bed) over 6 weeks. The dependent variables were pain and discomfort measured by 20 points visual analog scales, and range of extension and flexion measured by goniometery. The data were analyzed by descriptive statistics and repeated measures ANOVA. The results were as follows ; 1) There were significant differences for pain(F=9.77 p=.0001), discomfort(F=8.07 p=.001), range of extension(F=3.05 p=.05), and flexion(F=9.67 p=.0001) among heat therapy application times. 2) There were significant differences for pain(F=58.18 p=.0001), discomfort(F=63.68 p=.0001), range of extension(F=11.59 p=.001), and flexion(F=17.59 p=.0001) between before and after applying heat therapy. 3) There were not statistically significant differences for pain(F=.64 p=.531), discomfort(F=.18 p=.836), range of extension(F=1.33 p=.270), and fiexion(F=.26 p=.773) between before and after applying heat therapy according to the heat therapy application times. In conclusion, heat therapy was effective in reducing pain and discomfort, and in improving ROM for the elderly with osteoarthritis, but the effect of it was not different according to the time of application. We recommended further studies with larger sample size, longer and more repeatedly applied to investigate the effect of heat therapy according to the time of application.