Woody cells develop secondary wall structure that mainly consists of polysaccharides (cellulose and hemicellulose) and lignin. These components are expected to be new sources of biofuels and biomaterials. Therefore, it is important to understand the molecular mechanism underlying secondary wall formation and how it contributes to plant biomass. Plant-specific NAC domain transcription factor family has been shown to be involved in diverse biological functions. Recently, several studies reported that a subfamily of the NAC domain transcription factors plays pivotal roles in secondary wall formation. In this review, we have summarized the role of NAC domain transcription factors in controlling the secondary wall formation.