The purpose of this study was to develop a portfolio assessment program for elementary school third grade music classes. For the purpose, the study inquired theories of portfolio development and explored how to (1) setting goals and objectives for developing the portfolio assessment program, (2) devising contents of portfolio assessment and evaluation an developing assessment tools, (3) planning evaluation results from the portfolio, and application of the portfolio. The procedure of the portfolio program development was as follows: (1) A preliminary program for portfolio assessment was designed for the third grade classes of E elementary school, based on the content of the Curriculum of Music for Elementary Schools, and the students` musical experience. (2) The preliminary program for portfolio assessment was applied to the third grade music classes at E elementary school, and revised on the results of the applications. (3) The final portfolio assessment program was completed by amending the preliminary program through the results of the second procedure. This study found certain conclusion from developing a portfolio assessment program. Using the portfolio it allows teachers to improve their instruction through integrating teaching and evaluation simultaneously. It also provides a chance to practice a variety of learning methods such as individual learning, group learning, or interaction learning. Portfolio assessment also allows students to participate more actively in learning by various types of interaction. It also stimulates more reflective thinking so that the students have an insight into their learning process.