Regression testing is an essential and expensive activity in the maintenance phase to show that the code has not been affected by the changes. It consumes 80% of the maintenance cost. Hence optimizing the regression testing will be the prime motives for the software testers. We prioritize the test case based on number of the modified lines the test case covers. The test case that covers the maximum number of the modified lines is given highest priority, and executed first. Hence even if testing is not completed we can cover maximum number of modified lines. The test cases prioritization is done by using genetic algorithm. It takes the test case information as input and it produces a sequence of the test case that has to be executed so that maximum number of the modified code gets covered.