Background: Facial isometric exercise is a static contraction of facial muscles without any visible movement in the angle of the joints. To examine the effects of facial isometric exercise on subjective stress and oxidative stress/antioxidant capacity. Methods: In this study, we included 13 participants (6 males, 7 females; average age, 44.8 ± 19.6 years; age range: 20 - 74 years) who were exposed to constant temperature and humidity in a room. Fifteen minutes after entering the room, the force was measured before and after facial isometric exercise of the target muscles: upper lip levator, small zygomatic, large zygomatic, levator animus, laughing, buccal, muzzle, mental, temporal, masseter, and cervical muscles), and further evaluated by comparing the facial isometric exercise group and control (non-facial isometric exercise) group (crossover test). Results: Subjective stress significantly improved by 8.7 ± 16.3 in the facial isometric exercise group, and no significant difference in oxidative stress level was observed in both the groups. However, the antioxidant capacity significantly increased by 126.8 ± 168.1 μmol/l in the facial isometric exercise group. Conclusion: The results of this study suggest that facial isometric exercise is an exercise therapy that can provide mental stability and antiaging effects due to improvement in subjective stress and biological antioxidant potential.