We report on the effect of substrate miscut on the 2-dimensional interfacial structure and dielectric properties of the epitaxial Ba0.6Sr0.4TiO3/MgO. Epitaxial Ba0.6Sr0.4TiO3 films on vicinal (001) MgO grown by pulsed-laser ablation were studied using transmission electron microscopy (TEM). Plan-view TEM showed that the films grown on the substrate with miscut angles of 1.2 degrees 3.5 degrees and 5.3 degrees have lattice mismatches of -5.6%, -6.0% and -5.7% at the interface, larger than the values (-5.4%, -5.7% and -5.5%, respectively) obtained using cross-section TEM. The films grown on 1.2 degrees and 5.3 degrees miscut substrates consist of commensurate domains with sizes about 30 to 40 nm at the interface, significantly larger than those of 10 to 20 nm obtained for the films grown on the 3.5 degrees miscut substrate. The films with larger commensurate domains at the interface exhibit about 30% higher dielectric constant and dielectric tunability than those with smaller commensurate domains. Initial measurements show that their interfacial differences have a tremendous effect on the dielectric properties of the films. (C) 2009 Elsevier B.V. All rights reserved.