This paper presents a novel approach of test case regeneration for web applications. The proposed technique automatically multiplies original test cases with 2 types of multiplication operators: input value and behavior, to improve the fault detection effectiveness of the original test suite. Different from previous works, our approach is black-box and needs neither information of server-side source code nor transition diagrams of the application’s GUI states, and thus easily applicable. We implemented our approach and conducted experiments using 4 real world web applications. 22 faults in 4 applications were detected, and all of the faults were not revealed by the original test suites. Experimental results also show that the proposed technique achieves better effectiveness in terms of mutation score.