The microstructure of epitaxial SrRuO3 thin films grown on vicinal (001) SrTiO3 substrates with miscut angle of 1.9° and miscut direction of 12° away from  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//SrTiO3 and SrRuO3[1¯10]//SrTiO3. 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  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. © 1998 American Institute of Physics.