Abstract: In a previous study, we found that Hypericum perforatum seeds exhibit both exogenous and endogenous dormancy and the seeds needed light for germination strictly. In this study, the effect of light was studied more deeply. For this, seeds were exposed to different light intensities (0, 600, 1200, 1800 and 2400 lux) for 6, 12, 18 and 24 h a day. According to the results, the effect of light intensities was more evident and 2102.5 lux light intensity with any exposure times evaluated in this study except for 6 h a day was found to be the most suitable treatment for breaking endogenous dormancy.