This is an action research on implementing portfolio assessment in the course of The Principles of Instruction in Hualien Teachers' College. The results showed that there are twelve advantages and six disadvantages for the students, and three advantages and one disadvantage for the teacher. The advantages for students are the following: 1. It helps students own the complete learning files for them to recall in the future. 2. It develops students' abilities in collecting and organizing data. 3. It helps students understand and encourage each other. 4. It helps students become active in learning. 5. It compels students to learn by themselves. 6. It helps students reflect on their own leaning process. 7. It helps students understand the usage and advantages of portfolios and be willing to use them in their future learning. 8. It is a better evaluation form. 9. It proves students' efforts and existence. 10. It expresses students' ideas. 11. It helps students reflect on education policy. 12. It helps students establish their own data bank. The disadvantages for students are the following: 1. Students don't know how to look up and organize data. 2. There are conflicts between portfolio sharing and evaluation. 3. There are doubts in evaluation fairness. 4. It is tedious. Students spend a lot of time and money. 5. The portfolio file is too heavy and takes up too much space. 6. Students worried about their portfolio files. 7. Time is too short. The advantages for the teacher are the following: 1. Evaluation becomes a kind of learning and enjoying. 2. Teachers can understand students' learning process and learning methods. 3. Students become active in learning. The only disadvantage for the teacher is too time-consuming. However, it is a fatal defect for implementing portfolio assessment. It needs more researchers and teachers to work out.