Atomic structures and electronic states of epitaxial graphene on the SiC(11-20) a-face are studied based on the first-principles calculation. It is found that the surface can have two types of the surface, the stable quasi-free-standing structure and the quasi-stable buffer layer structure. The neutral nature, the low interface state density, and the absence of large interface dipoles suggest that the epitaxial graphene on the SiC(11-20) a-face is appropriate for studying the physical properties of carrier transport. It is also proposed that the existence of the buffer layer is directly related with the epitaxial relation of the formed graphene with the SiC substrate. [DOI: 10.1380/ejssnt.2016.113]