This article is devoted to using portfolio in evaluation process of students’ knowledge of studying the course "Calculus". Portfolio as a method of qualitative and comprehensive approach to knowledge assessment is gaining great importance. With the portfolio method, the assessment process becomes focused and continuous. The portfolio allows you to build the learning process taking into account the individual characteristics of each student. The portfolio method allows you to take into account all the student’s achievements in acquiring new knowledge, developing personal and professional competencies. The benefits of portfolio method are examined in the context of mathematics education, emphasizing the portfolio method's ability to systematize and to document students' individual achievements and progress. The article also covers the issues of choosing content and portfolio structure, evaluation methods and influence in the learning process. Aspects of introducing portfolios into the learning process for an accurate and comprehensive assessment of students' knowledge in Calculus have been studied.