Glycidyl ether polyhedral oligomeric silsesquioxanes (POSS-EP) was prepared in high yield by hydrolysis and condensation of 3-glycidyloxypropyltrimethoxysilane (EPTMS). Through a thermal copolymerization between G4 PAMAM dendrimers and blends of POSS-EP and bisphenol A epoxy resin (DGEBA), a series of epoxy-based POSS/PAMAM hybrid materials was obtained. Thermal copolymerization reaction was characterized by differential scanning calorimetry (DSC) and a reaction activation energy (Ea) was calculated by Kissinger’s model. Thermal and mechanical properties for the hybrid materials obtained under different copolymerization conditions were studied by DSC, thermogravimetric analysis (TGA) and tensile test. The results revealed that owing to the presence of POSS groups and the specific role of structure-properties relationship for PAMAM tree-structure, these epoxy-based POSS/PAMAM hybrid materials exhibited excellent thermal stabilities and mechanical properties.