Students ability to build correct knowledge relies on their understanding of concepts. Students must understand the concept well before applying it in real-life situations. With the advent of technology, teaching and learning quantum physics has been made easier and more effective in enhancing students' critical thinking and conceptual understanding. A multimedia-based learning approach is one way to enhance conceptual understanding. With the help of the multimedia application, this study aims to assess its impact on students' conceptual understanding of quantum physics at the University of Rwanda College of Education (UR-CE). The study adopted a quasi-experimental pre-test--post-test design with control and treatment group. Three hundred eighty-five undergraduate students in the UR-CE were purposively selected and allocated into the treatment group (193 students) and the control group (192 students). Control group students were taught eight quantum physics topics for six weeks using the traditional teaching approach, while treatment group students were taught the same topics using animations, PhET simulations, and YouTube videos. The study resulted in a very high statistically significant difference (p < 0.001) between teaching interventions provided after post-testing in favor of students who learned with multimedia (with a large effect size of 0.694). The use of multimedia resulted in a statistically significant increase in the student's conceptual understanding of quantum physics. The study's findings suggest that multimedia tools are effective for learning because they can enhance students' conceptual understanding of quantum physics. However, interactions between teachers and students or student-to-student are essential to facilitate conceptual learning and help the students gain a valuable understanding of their learning.