The use of summative assessment methods revealed limitations in encouraging pre-service primary teachers (PsTs) to become deeply involved in their professional training. Ut has been suggested that the use of portfolios as a learner-centred assessment approach can stimulate PsPs' professional competence. A study of applying portfolio assessment on a class of 83 pre-service primary teachers within the Micro-teaching course of Primary Science Education was carried out. The results showed that the portfolio-based assessment definitely improved PsTs' professional competences in terms of Pedagogical Behaviour, Professional Knowledge and Skills.