Social media is becoming more popular, and its resourcefulness has given students new opportunities to learn as well as broaden their academic horizons in various ways assumed if social media is handled appropriately. The main purpose of this study was positioned to estimate the predictive mediating effects of social media on the relationship between students' engagement and academic achievement of undergraduate university students. In doing so, a correlation study design was employed. Data was collected from 395 participants who were selected through a simple random sampling technique. Structural equation modelling was used to analyze the study data. As a result, the study findings showed both social media and student engagement has a significant direct effect on academic achievement. However, when social media entered the structural relationship between students' engagement and academic achievement as a mediator variable, the mediating effect was no longer significant, indicating social media played a direct-only non-mediation role. This may be due to social media allowing for students' minimal engagement. The result demonstrates the need for critical consideration when social media and instruction incorporated into educational activities for students' benefit. This suggests more research is required to confirm the all-round effects of how social media influence students' engagement in learning, even though in some literature the results are encouraging. More initiatives are essential because they may reveal efficient intervention tactics for integrating social media into higher education systems.