The ground-level ozone (O₃) concentration has been increasing, especially in Northeast Asian region. Elevated O₃ suppresses growth and inhibits many physiological processes including stomatal reactions, photosynthetic, and the nutrients translocation or storage in tree species. Japanese larch and its hybrid larch F₁ have been major species at the artificial forest in Asian countries due to the higher growth rate and adaptability to the harsh condition. In this study, these two larch seedlings were exposed to four O₃ levels [ranging from 10 to 60 nmol O₃ mol^-1] in open-top chambers (OTCs) for two consecutive growing seasons. Higher O3 declines growth and inhibits the physiological process of both larches. However, we found significant hormetic responses in physiological reactions at the relatively lower O₃ level. Hormesis means that low levels of exposure favourably stimulate the performance of organs but its high levels of exposure negatively inhibit the performance. Also, the species difference responses were observed. As responses at an individual level, similar responses were founded only in Japanese larch but hybrid larch F₁ although there were no significant changes. These findings are the first to suggest that stimulation of physiological functions by low O₃ exposures may have negative consequences for the larch plantation.