Isometric exercises are effective in reducing knee pain and improving functional ability among elderly with osteoarthritis. The aim of the study was to identify the effect of isometric exercise on functional ability among elderly with osteoarthritis at selected old age home at Coimbatore. Quasi-experimental one-group pre-test–post test design was adopted in this study. Twenty-two elderly were selected by using purposive sampling technique. The demographic profiles were collected from the elderly. Pre-test was done to assess the knee pain, stiffness and physical function by using WOMAC index scale. Aerobic exercises were given to elderly for 10 minutes. Isometric exercises were administered followed by aerobic exercises, twice daily for 30 minutes for 30 days. Post-test was done to assess the knee pain, stiffness and physical function among elderly with osteoarthritis by using WOMAC index scale. It was identified that the mean level of functional ability before and after isometric exercises were 38.01 and 34.9, respectively, with a mean difference of 3.11. Standard deviations were 10.91and 7.41. The calculated t- value 2.24 was greater than the table value at 0.05 level of significance. Hence, it was concluded that isometric exercise is an effective intervention in improving functional ability among elderly with osteoarthritis.