The goal of this study is to devise a test that measures developmental music aptitude for children under age 8, which is critical for the development of music aptitude. We revised the first version of the test, because it had some problems with using at schools. The revised test is called Kids' Music Aptitude Test(Kids' MAT). It is a test of melody and rhythm and has 40 items. The test has been administered four times to children of age 5-7. The items have been revised several times based on the statistical analysis. Moreover, the test has been revised based on the following observations: (1) The recorded instructions should be short as far as possible; (2) Example items should be devised and used; (3) It should be verified whether children have understood the instructions; (4) The pictures in the answer sheet should be agreeable by everybody; (5) It is impossible for children to concentrate more than 20 minutes; (6) For children aged 5, the test should be administered individually or with one teacher assigned to less than 5 children. This study is in progress. The test is incomplete in several aspects because it tries to measure music aptitude of young children. Better test items should be devised by means of more experiments. Studies for concurrent validity and predictive validity should be conducted.