<p>The objective of this study is to explore the mediating effect of learning engagement on the relationship between learning self-efficacy, learner interaction, emotion regulation, and perceived learning among Chinese secondary school students in an online mathematics learning environment. This research adopted a quantitative approach with a predictive correlational design, involving 605 participants selected through simple random sampling. Structural Equation Modelling (SEM) was employed to analyse the collected data. The SEM analysis revealed a significant positive relationship between learning self-efficacy, learner interaction, emotion regulation, and perceived learning. Bootstrapping results indicated that learning engagement partially mediates the relationships between learning self-efficacy and perceived learning, learner interaction and perceived learning, as well as emotion regulation and perceived learning. These findings enhance our understanding of the critical roles that learning self-efficacy, learner interaction, emotion regulation, and perceived learning play, with learning engagement acting as a mediator in the context of online mathematics learning.</p>