Although the chemical literature contains many studies of multimedia-based learning and teacher enthusiasm, there is a paucity of research on whether and to what extent teacher enthusiasm in video lectures affects students' learning, especially in chemistry. In this context, this mixed-method study used eye tracking and quantitative analysis to investigate how a teacher with different levels of enthusiasm influenced students' learning in video lectures. Junior middle-school students were selected to engage in this eye-tracking research. We set up 35 such students as a group to view an experimental video with a low level of teacher enthusiasm, and 35 others as another group to view another experimental video with a high level of teacher enthusiasm. The essential tool for capturing the students' visual attention was an EyeLink 1000 Plus eye tracker. The total dwell time, fixation counts, average fixation duration, and transition counts were recorded and analyzed, and the results showed that the teacher enthusiasm in the video lectures had an indirect positive effect on the students' self-efficacy and learning performance and was negatively associated with cognitive load. In addition, students paid more attention to the teacher with the higher level of enthusiasm.