We investigated the effects of annealing on the rearrangement of the H-bond network microstructure and its influence on the thermal and rheological properties of the second pseudo-generation hyperbranched (HB) polyester based on 2,2-bi.s(methylol)propionic acid (Boltorn H20) in comparison to the fourth pseudo-generation HB polyester (Boltorn H40). During annealing the hydroxyl groups of HB polyesters form H-bonds with other hydroxyl or carbonyl groups. The formation of -OH...-OH H-bonds is favored at shorter annealing times, higher annealing temperatures, and for low pseudo-generation HB polyester, which has a low average molar mass, degree of branching, and core functionality. At temperatures up to 80 degrees C, Boltorn H20 indicates faster and more extensive H-bond formation as compared to Boltorn H40. This is reflected in its larger cleavage enthalpies and higher elastic contribution to the viscoelastic response. At 90 degrees C and above, the process of H-bond formation is delayed. Therefore, Boltorn H20 exhibits only viscous behavior in rheological measurements, and in DSC curves it shows strong exothermic transitions while heating the sample.