This study aimed to investigate the effect of the online PhET simulation-assisted using the direct instruction on students’ conceptual understanding of the parabolic motion. It was quasi-experimental research with pretest-posttest control group design. The research subjects were 10th grade students, consisting of 20 students for each experimental and control groups. The data were collected using a concept understanding test. The research data were analyzed quantitatively by using descriptive and inferential statistics. The results show that the average score of the experimental class was higher than the control class. The hypothesis was tested using Mann-Whitney (U-Test) with a significance level of = 0.05. Based on data analysis, it can be concluded that there was a significant effect of online PhET simulation assisted learning model on students’ concept understanding on parabolic motion.