This study aims ata improfing student s writing in terms of content organization and language use through the implementation of portfolio assessment. This classroom action research is descriptive qualitative in nature and was conducted in only one cycle consisting of four stage activities. Twenty-six students taking Writing II course ware teken as the subject and the main data was the paragraphs the students wrote throughtout semester. The instrumen of data collection include rubric self-reflection sheet field notes and questionaire.