Solid-state NMR techniques were used to evaluate the sizes of the dispersed domains and the interface between the minor and the major phase in heterogeneous block copolymer systems with a relatively poor degree of ordering. Proton spin-lattice relaxation measurements and spin diffusion experiments were carried out on five samples of linear and star block copolymers of styrene, styrene-co-indene, and isobutylene. The morphology of the dispersed phase was considered cylindrical for all samples. The diameters of the dispersed cylinders were found to range between 7.9 and 48.5 nm for the linear samples and 22.6 nm for the star block copolymer sample. The thickness of the interface was estimated to be between 1.0 and 1.3 nm for all samples. SAXS measurements were employed to confirm the validity of the NMR data analysis.