Blends of poly(L-lactic acid) (PLA) and poly(butylene succinate) (PBS) were prepared with various compositions by a melt-mixing method and the phase behavior, miscibility, and morphology were investigated using differential scanning calorimetry, wide-angle X-ray diffraction, small-angle X-ray scattering techniques, and polarized optical microscopy. The blend system exhibited a single glass transition over the entire composition range and its temperature decreased with an increasing weight fraction of the PBS component, but this depression was not significantly large. The DSC thermograms showed two distinct melting peaks over the entire composition range, indicating that these materials was classified as semicrystalline/semicrystalline blends. A depression of the equilibrium melting point of the PLA component was observed and the interaction parameter between PLA and PBS showed a negative value of -0.15, which was derived using the Flory-Huggins equation. Small-angle X-ray scattering revealed that, in the blend system, the PBS component was expelled out of the interlamellar regions of PLA, which led to a significant decrease of a long-period, amorphous layer thickness of PLA. For more than a 40% PBS content, significant crystallization-induced phase separation was observed by polarized optical microscopy.