Alternative assessment plays an important role in gathering information about students' learning. Introduction of new curriculum in Malaysian primary school education namely Standard Curriculum of Primary School has highlighted portfolio as an assessment tool. Therefore, research has been conducted to examine teachers' understanding towards this new alternative assessment method. The qualitative data used in this research were gathered from three interview sessions and classroom observations. Five primary school teachers were selected as participants of this research. They are teaching core subject such as English, Mathematics and Science. Thematic analysis was conducted to examine the themes emerged to represent their understandings towards portfolio. Teachers' understandings towards portfolio were grouped into three major themes: As students' work collections, as feedback and improvement tools and as teaching, learning and grading tools. They used portfolio in classroom as they understood. Different understandings were revealed as these teachers are also teaching different subjects. This may be the reason why these teachers were having different understandings towards portfolio assessments. This research is significant to teachers, stakeholders, school administration and even society about portfolio assessment.