In the present work, we report our work concerning the synthesis of heteropolymers of poly(epsilon-caprolactone)-polyoxomolybdate-poly(epsilon-caprolactone) using ring-opening polymerization (ROP) of epsilon-caprolactone monomer initiated by two hydroxyl groups attached on the two sides of a polyoxomolybdate cluster which was organically modified using pentaerythritols. Since the hydroxyl groups on polyoxomolybdate macroinitiator are less reactive, ring-opening polymerization were finally carried out by using 4,4'-(dimethylamino) pyridine to activate epsilon-caprolactone monomer. The polyoxomolybdate-containing heteropolymers were confirmed in detail by H-1 NMR, FT-IR, GPC, TGA and XPS methods. Although the size of polyoxomolybdate cluster is extremely small compared to PCL chains, it was also found that POM played an important role in crystallization process. Self-assembly of such heteropolymers in mixed solvents were investigated and the analysis of formed spherical aggregates with multiple concaves on the surface was supported by TEM results and 3D electron tomography. (C) 2011 Elsevier Ltd. All rights reserved.