N6-methyladenosine (m⁶A) is the most common and abundant modification in RNA molecules present in eukaryotes. The m⁶A modification is catalyzed by a methyltransferase complex METTL3 and removed by the recently discovered m⁶A RNA demethylases FTO and ALKBH5, which catalyze m⁶A demethylation in an α-ketoglutarate (α-KG)- and Fe2+-dependent manner. It was shown that METTL3, FTO, and ALKBH5 play important roles in many biological processes, ranging from development and metabolism to fertility. m⁶A accounts for more than 80% of all RNA base methylations and exists in various species. m⁶A is mainly distributed in mRNA and also occurs in non-coding RNA such as tRNA, rRNA, and snRNA. The relative abundance of m⁶A in mRNA transcripts has been shown to affect RNA metabolism processes such as splicing, nuclear export, translation ability and stability, and RNA transcription. Abnormal m⁶A methylation levels induced by defects in m⁶A RNA methylase and demethylase could lead to dysfunction of RNA and diseases. For example, abnormally low levels of m⁶A in target mRNAs due to increased FTO activity in patients with FTO mutations, through an as-yet undefined pathway, contributes to the onset of obesity and related diseases. The dynamic and reversible chemical m6A modification in RNA may also serve as a novel epigenetic marker of profound biological significance. Therefore, more useful information for a better understanding of m⁶A RNA methylation levels and distribution on RNA transcripts could benefit diagnostics and therapeutics of disease.