Test case prioritization is an effective and practical technique that helps to increase the rate of regression fault detection when software evolves. Numerous techniques have been reported in the literature on prioritizing test cases for regression testing. However, existing prioritization techniques implicitly assume that source or binary code is available when regression testing is performed, and therefore cannot be implemented when there is no program source or binary code to be analyzed. In this paper, we presented a new technique for black box regression testing, and we performed an experiment to measure our technique. Our results show that the new technique is helpful to improve the effectiveness of fault detection when performing regression test in black box environment.