We propose a model-based regression test case prioritization technique for object-oriented programs. Our technique involves constructing a graph model of the source code to represent control and data dependences as well as static object relations such as inheritance, aggregation and association. We construct a forward slice of the model to identify all the model elements that may be affected by a change. Subsequently, the model elements are marked with the specific test case(s) testing it. We construct backward slice with respect to each model element executed by a test case to determine all elements indirectly tested by the test case. Then all the affected model elements and the elements being tested are used to prioritize test cases. Empirical studies carried out by us show that our technique increases the detection of number of faults on an average of 30 percent as compared to traditional approaches in detecting regression errors