Prolonged viewing of videos in virtual reality environments induces visual and cognitive fatigue in users. This paper presents a method of predicting fatigue from watching virtual reality videos. The proposed method uses a camera to measure eye movements, pupil size changes, and blink rates and intervals, to estimation the degree of fatigue using a random forest. The prediction results are annotated using a standardized chart and then aligned to subjective fatigue evaluations for validation. This study will provide foundational data for enhancing VR user experience, by developing fatigue management capability and optimizing wearability and playability of VR contents