Software testing is an important step in the software process. It makes the developed software more accurate and reliable. Generating test cases is a key element in the process of software testing. The quality of testing depends on the test effectiveness. This paper presents a method for generating test cases using genetic algorithms. A test case generation tool is developed with Visual Basic .NET for supporting our method. The proposed method was applied on case studies and mutation testing was used in our experiment for performance evaluation. The results show that the generated test cases are appropriate for software testing