Teacher enthusiasm is known to affect students' learning in traditional classroom environments, but it is unclear how displayed teacher enthusiasm can optimize learning of chemistry procedural knowledge in multimedia learning environments. In this context, the present study used eye-tracking technology and quantitative analysis to examine how displayed teacher enthusiasm in video lectures affects students' positive emotions, visual attention, cognitive load, and learning outcomes. Measures were collected from 128 eighth-grade middle school students. An EyeLink 1000 Plus eye-tracker was used to capture the students' eye movements. The percentage of total fixation duration, percentage of fixation count, mean pupil size, and blink rate were used as metrics to analyze the eye-gaze data. The results showed that an enthusiastic teacher positively affected students' positive emotions, reduced students' cognitive load, and made students more concentrated on the learning-content area. Additionally, the higher level of displayed teacher enthusiasm improved learners' learning outcomes.