The microstructure of epitaxial SrRuO3 thin films grown on vicinal (001) SrTiO3 substrates with miscut angle of 1.9 degrees and miscut direction of 12 degrees away from [100] direction was studied using transmission electron microscopy (TEM). Cross-section as well as plan-view TEM studies revealed that these films are single domain with the in-plane epitaxial orientation relationship of SrRuO3[001]//SrTiO3[010] and SrRuO3[(1) over bar 10]//SrTiO3[100]. This result is in contrast to the previous studies of the SrRuO3 thin films grown on exactly (001) SrTiO3, which are composed of two types of [110] domains with nearly the same volume fraction. The occurrence of these different domain structures is attributed to the step-flow growth of the film on the substrate surface due to the miscut. (C) 1998 American Institute of Physics.