This research is a case study that seeks to reveal teachers' perceptions of portfolio assessment in primary schools in Indonesia. The research sample was 20 elementary school teachers in Central Java Province, Indonesia, representing senior teachers, master teachers, young teachers, and junior teachers. Data collection used depth interviews which were designed based on 10 powerful portfolio assessment principles. Qualitative data analysis was performed using interactive data analysis which included condensation data, display data, and conclusion. The results were showed that 6 of 10 principles of portfolio assessment were approved by the majority of teachers, while others were not. Two principles, namely the effectiveness of time and energy (principle 2) and portfolios as a new learning perspective (principle 8) are rejected by most teachers in Indonesia. The two other principles, namely the importance of teacher cooperation in portfolio assessment (principle 3) and the role of portfolio assessment as self-evaluation (principle 9) received low approval scores. The obstacles for the teacher to carry out the portfolio assessment are the problem of the length of time it takes, the large number of elementary school students in a class, and the teacher's low insight into portfolio assessment. Research recommendations are that the success of portfolio assessment will be achieved if it is carried out in a structured and sustainable manner; it is necessary to carry out training and monitoring of teacher performance to maximize assessment, learning and evaluation of learning; and the need to adapt the e-portfolio assessment for primary schools.