Retrieval practice has been proved effective in conceptual science learning and retesting was applied in retrieval practice and showed significant improvement in learning outcomes (Karpicke & Blunt, 2011; Ariel et al., 2018; Lyle et al., 2020). In this study, retesting was employed in an online microbiology course to evaluate the attitude and behavior of college students about it. The students were offered the same course materials and requirements except for three different options: retesting in exams without practice quizzes, retesting in practice quizzes with points, or retesting in practice quizzes without points. Our data indicated that retesting improved the exam grades, especially in those with a longer interval period between two consecutive testing attempts. Not surprisingly, the points in practice quizzes encouraged more students to take practice quizzes and their exam grades were improved. Distractedly not all the students would utilize the retesting opportunities to enhance the retention of information, which could be associated with student engagement in distance learning.