Grayanotoxins are neurotoxins that are mainly produced by plants of Genus Rhododendron. Among the plants native to Korea, R. yedoense (royal azalea) and R. brachycarpum are widely known to contain grayanotoxins, R. mucronulatum (azalea), on the other hand, is known to be non-toxic and its flower has been widely eaten as food. However, a few azalea intoxication cases have been reported, showing the possibility of azalea toxicity. In this study, we tried to determine the cause of the reported azalea intoxication cases if they were caused by genuine toxicity of azalea or by royal azalea mistaken as azalea. Samples of three species of Rhododendron were collected and analyzed by LC-MS/MS to detect Grayanotoxin Ⅰ and Ⅲ. As a result, 4 out of 10 azalea flower samples contained grayanotoxins suggesting that some azaleas can cause grayanotoxin poisoning. To identify differences between the toxic and non-toxic azaleas, DNA barcoding was performed. By comparing their barcoding sequences of chloroplasts, it was found that the toxic azaleas contain DNA sequences which present in royal azaleas in rbcL region. The relationship between the change in rbcL region and synthesis of grayanotoxins is not clear, but it implies that more DNA changes could have occurred in the toxic azaleas to produce grayanotoxins. In conclusion, azalea flowers with DNA changes can cause grayanotoxin poisoning. Further studies on the DNA differences and the effect of environment on the expression of grayanotoxins are necessary to figure out the cause of the random toxicity by azalea.