New hyperbranched polymers (HBP) have been synthesized by reaction of a poly(ethylene imine) with phenyl and t-butyl isocyanates. These HBPs have been characterized by 1H-NMR (nuclear magnetic resonance of hydrogen) and Fourier transform infrared spectroscopy. Their influence on the curing and properties of epoxy-anhydride thermosets has been studied by different techniques: differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and thermogravimetry (TG). The curing kinetics has been studied with DSC. Integral isoconversional method and the S ¿ esta´k–Berggren model have been used to determine the activation energy and the frequency factor. The kinetic parameters are very similar for all the studied systems at the middle stage of the process, but changes are observed at the beginning and at the end of the process when these modifiers are used. The HBPs reduce the glass transition temperature of the cured materials. In addition, from the DMA analysis it can be seen that the HBP modifier obtained from phenyl isocyanate hardly changes the storage modulus, but the obtained ones from t-butyl isocyanate decrease it. TG analysis reveals a decrease in the onset temperature of the degradation process upon addition of the HBPs.