Abstract: UV spectrophotometry and TLC are applied to the purity test for cyclandelate. The limit test of ketoester in cyclandelate is 0.2 μg by TLC. The extinction coeffecience values at λmax 258nm are 10,600 and 207 respectively. They are overlapped in absorption spectrum and of great disparity in extinction coeffecience. Thus the content of ketoester has marked effect on the absorption of cyclandelate. This test shows that the ratio of absorption between λmax 252nm and 264nm will be a good parameter in the quality control of the cyclandelate.