Despite the fact that over 150 different types of RNA modifications have been found in all types of RNAs, the role of only a few RNA modifications has recently been demonstrated as an essential regulator of posttranscriptional gene expression during plant development and stress responses. Among them, N6-methyladenosine (m6A) methylation is the most abundant modification in messenger RNAs and has been shown to play essential roles in developmental process in plants as well as in animals. However, its role in plant response to abiotic stresses remains largely unknown. In this study, we aimed to determine the role of m6A RNA methylation in plant response to abiotic stresses. Analysis of knockdown mutants of m6A writer protein revealed that decreases in m6A methylation level strongly inhibited the seed germination of Arabidopsis under salt, dehydration, and heat stress, but not under cold stress. Moreover, seedling growth of the mutants was significantly inhibited by salt or heat stress, and leaf initiation of the mutants was delayed under cold stress. Notably, stability of several genes involved in stress response was affected by altered levels of m6A modification. Collectively, these results suggest that regulation of m6A RNA methylation is essential for plant adaptation to abiotic stresses.