This study highlighted the humanistic-transformational perspectives via portfolio assessment which offers a conceptual framework for teaching and assessment. More specifically, it attempted to explore the effectof portfolio assessment on EFL learners'reading comprehension ability and motivation in the context of Iran. It adopted the quasi-experimental design comprising the pretest-treatment-posttest paradigm. To achieve the purpose, the researchers collected the triangulated data about the participants. Two classes were selected as the experimental and control groups from Tabaran Institute of Higher Education. They were 65 female university students majoring in translation. The only difference between the two groups was integrating portfolio into learning strategy-based instruction for the experimental group (portfolio-based instruction vs. non-portfolio instruction). At the post-testing stage, the both groups were retested through the reading comprehension test and the motivation questionnaire. A self-report assessment was also utilized to increase the credibility of the motivation test. The result obtained from Mann Whitney U tests and t-tests revealed that portfolio assessment as a constructivist strategy empowers participants' reading comprehension and motivation.