Curing as well as the phase separation behavior of blends of a hydroxy-functionalized hyperbranched polymer (HBP) and epoxy resin have been studied by several techniques. The HBP strongly enhance the curing rate due to the catalytic effect of hydroxy groups. The phase separation has been investigated for various HBP contents and as a function of cure conditions used as well. The thermal and dynamic viscoelastic behavior of the blends have been examined and compared to the unmodified epoxy matrix. Finally, impact properties have been discussed in terms of the morphological behavior for an epoxy matrix modified with various amounts of HBP.