Constructionism, one of the cognitive learning theories, is based on the contention that knowledge is not directly transmitted from teachers to students but is constructed by students themselves through their interactions with the environment. Portfolio has a potential to be an authentic assessment tool to assess student learning. It not only assesses what students have learned in complex, real-world situations, but also serves as an effective learning tool for students itself. This article aims to present the essential details of the portfolio as an assessment method and a learning tool for students in constructionist learning environment; therefore, it provides readers with the concept of constructionism and constructionist learning, the concept of portfolio, types of portfolio, processes of portfolio development, and an example of using portfolio assessment in constructionist learning environment.