Small fixed aggregates of a poly(ethylene oxide)-block-polybutadiene diblock copolymer (PEO-b-PB) in THF solution were obtained by adding a selective solvent for PB blocks, followed by cross-linking the PB shells. The morphologies of the nanostructured particles with a cross-linked shell were investigated by atomic force microscopy and transmission electron microscopy. The average behaviors of the PEO crystallization and melting confined within the nanostructured particles were studied by using differential scanning calorimetry experiments. For the deeply cross-linked sample (SCL-1), the crystallization of the PEO blocks was fully confined. The individual nanoparticles only crystallized at very low crystallization temperatures (Tcs), wherein the homogenous primary nucleation determined the overall crystallization rate. For the lightly cross-linked sample (SCL-2), the confinement effect was Tc dependent. At Tc ≤ 42℃, the crystallization and melting behaviors of SCL-2 were similar to those of the pure PEO-b-PB diblock copolymer. At Tc > 42℃, SCL-2 could form PEO lamellae thicker than those of the pure PEO-b-PB crystallized at the same Tc.