The structure buildup in hyperbranched polyesters from 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) was studied experimentally. Bis-MPA and its dendritic trimer were both polymerized in bulk using acid catalyst. The fractions of terminal, dendritic, and linear repeating units were monitored by C-13 NMR during the course of reaction. Effect of slow monomer addition on the degree of branching in the final product was also studied. Hyperbranched polymers from bis-MPA with and without a core molecule were kept at the polymerization temperature in order to examine the effect of heat treatment on composition in the polymer. The fractions of the different repeating units were changing to a large extent with conversion. Slow monomer addition to a trifunctional core molecule gave a product with a degree of branching of 47%. Heat treatment of hyperbranched materials gave small changes in the fractions of the different repeating units in both materials and, eventually, gelling in the material without a core.