This study aims to examine the impact of mathematics teaching supported by virtual manipulatives in an online learning environment on the academic achievement of primary school 4th grade students. In the study using a mixed method, experimental (n=24) and control (n=24) groups were established. While the experimental group was taught online with virtual manipulatives based on the Realistic Mathematics Education approach, traditional methods were employed for the control group. Mathematics academic achievement test and semi-structured interview forms were used as data collection tools. While the quantitative data were analyzed using independent samples t-test, the qualitative data were analyzed by the descriptive analysis method. The findings indicated that the academic achievement of the students in the experimental group increased significantly compared to the control group (p<0.05). In addition, the experimental group students reported that the virtual manipulatives used in the online environment enhanced their conceptual understanding, increased their motivation and facilitated their mathematics learning. As a result, it has been revealed that teaching practices using virtual manipulatives and real-life examples in the online learning environment make positive contributions to students' mathematics learning, although some students require additional support.