We investigated the effects of the sintering atmosphere on the interface structure and grain-growth behavior in 10-vol%-YAG-added Sic. When alpha-SiC was Iiquid-phase-sintered in an Ar atmosphere, the grain/matrix interface was faceted, and abnormal grain growth occurred, regardless of the presence of a-seed grains. In contrast, when the same sample was sintered in N-2, the grain interface was defaceted (rough), and no abnormal grain growth occurred, even with an addition of a-seed grains. X-ray diffraction analysis of this sample showed the formation of a 3C (beta-SiC) phase, together with a 6H (alpha-SiC) phase. These results suggest that the nitrogen dissolved in the liquid matrix made the grain interface rough and induced normal grain growth by an alpha -beta reverse phase transformation. Apparently, the growth behavior of SiC grains in a liquid matrix depends on the structure of the grain interface: abnormal growth for a faceted interface and normal growth for a rough interface.