Molecular mobility and phase structure of biodegradable poly(butylene succinate) (PBS) and poly(butylene succinate-co-20 mol % butylene adipate) [P(BS-co-20 mol % BA)] have been investigated by high-resolution solid-state C-13 NMR. For both samples, two components with different C-13 spin-lattice relaxation time (T-1C) values have been observed in the crystalline region. The crystalline component with shorter T-1C value is assignable to the interface near amorphous phase. The crystalline component with longer T-1C value is ascribed to the inside of the crystalline region. On the basis of T-1C, it has been concluded that the BA units are not included in the crystalline region of P(BS-co-20 mol % BA). Molecular mobility and higher-ordered structure of amorphous phase have been also compared between the melt and solid state. Variable-temperature high-resolution C-13 NMR measurements for the amorphous phase have revealed the remarkable difference in dynamics and structure between the melt and solid state.