The aim in this study was to evaluate the effect of local heat application on pain, stiffness, physical function and quality of life in patients with knee osteoarthritis. Local heat application is used as a non-pharmacological practice for the treatment of knee osteoarthritis. On the other hand, literature reveals limited information on the effects of heat application. The study was a comparative study. The patients with knee osteoarthritis were divided into two groups (23 patients in each) as intervention and control groups, and patients in the control group were applied with the routine medication of the physician. The intervention group received 20-minute heat application every other day for four weeks in addition to the routine medication. The data were collected using data collection form, Western Ontario and McMaster Universities Index and SF-36. The Western Ontario and McMaster Universities pain and Western Ontario and McMaster Universities disability scores of the patients with knee osteoarthritis in control and intervention groups before and after the intervention were compared, and the differences for both scores in the change were found to be statistically significant (p < 0.05). Moreover, statistically significant differences were found between the control and intervention group patients in terms of changes in the scores for physical function, pain and general health perception (p < 0.05). It was found that heat application every other day decreased pain and disability of the patients with knee osteoarthritis. Also, heat application was found to improve the subdimensions of quality of life scores of physical function, pain and general health perception of patients. The data obtained in this study on the efficiency of heat application on pain, stiffness, physical function and general health perception of patients with knee osteoarthritis may offer an insight into decision-making process for appropriate intervention.