Objective : To evaluate the effect of heat and steam generating sheets on osteoarthritis of the knee. Methods : Subjects with osteoarthritis of the knee (n=41) were randomized into 2 groups : a heat and steam generating sheet group or a heat generating sheet group. Functional impairment [Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Japan Orthopaedic Association score (JOA score)] in the index knee were measured at baseline and then again after 2 and 4 weeks of wear. Results : At both the 2 and 4 week patient evaluations, the heat and steam generating sheet group showed improved total WOMAC scores. Although the heat generating sheet groups' WOMAC scores were improved after 2 weeks, the difference between the 2 and 4 week evaluations was not statistically significant. As for individual WOMAC scores, patients in the heat and steam generating sheet group especially demonstrated a highly significant decrease in WOMAC stiffness score. In comparison, patients in the heat generating sheet group showed no improvement in WOMAC stiffness score. Gait ability improvement, as measured by JOA score, showed similar results for both groups. Conclusion : This study showed that using heat and steam generating sheets decreased pain and stiffness, and increased gait ability in patients with osteoarthritis of the knee.