Our study shows that the epitaxial growth of rhombohedral boron carbide, r-B4C films on the (0001 ̅ ) surface, but not on the (0001) surface of 4H-SiC is not due to interface roughening or formation of any interlayer. We cannot give a detailed atomistic explanation for the differences in the growth modes, but the experimental results develop the knowledge on the r-B4C/4H-SiC interface, the epitaxial r-B4C film and its growth morphology. We argue that epitaxial r-B4C film growth is hindered by carbon accumulation and poisoning of the growing surface.