Students’ conceptual understanding is the main outcome of all education in the world. Students must be able to understand the concept well in order to apply their knowledge in daily life. One of the efforts to improve the conceptual understanding is through computer based learning. This study aims to improve the students’conceptual understanding in physics by using virtual laboratory. The subjects were students from three different senior high schools. Students were divided into three experiment groups and three control groups. The research instrument used was in the  multiple choice form. The results showed that the use of virtual laboratory gave a positive effect toward students’ conceptual understanding. The final test result of the experimental group is higher than the control group. The data of this research were also analyzed based on the number of students' correct answers in every cognitive aspect. The result showed that in each school, students were able to answer  the questions correctly on aspects of C1 (remembering), C2 (knowing), C3 (applying) and C4 (analyzing). While on the aspects of C5 (evaluating) and C6 (creating) still needed to be improved.