AbstractRegression testing ensures that changes made in the fixes or any enhancement changes do not impact the previously working functionality. Whenever software is modified, a set of test cases are run to assure that changes don’t affect the other parts of the software. Hence all existing test cases need to be tested as well as new test cases need to be created. It is nonviable to re-execute every test case for a given software, because if there are more number of test cases to be tested, the more effort and time is required. This problem can be solved by prioritizing test cases. Test case prioritization techniques reorder the priority of a test case in an attempt to ensure that maximum faults are uncovered by the high prioritized test cases. In this paper we propose an optimized test case prioritization technique using Ant Colony Optimization (ACO) to reduce the cost, effort and time taken to perform regression testing and also uncover maximum faults.