The microstructure of epitaxialSrRuO3thin films grown on vicinal (001)SrTiO3substrates with miscut angle of 1.9° and miscut direction of 12° 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 ofSrRuO3[001]//SrTiO3[010]andSrRuO3[1¯10]//SrTiO3[100].This result is in contrast to the previous studies of theSrRuO3thin 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. ©1998 American Institute of Physics.