The precise stoichiometry required for the acetylation of surface amines of a poly(amidoamine) (PAMAM) dendrimer generation 5 (G5) was verified by using potentiometric titration, gel permeation chromatography, and nuclear magnetic resonance spectroscopy. The average number of primary amine groups, absolute molecular weight, and molecular weight distribution of G5 PAMAM were determined by potentiometric titration and GPC. These fundamental parameters were used to design the stoichiometry of an acetylation reaction that yielded acetylation fractions from 0 to 100% of the primary amines on the macromolecule. GPC refractive index detector confirmed that the diameter of the dendrimer related inversely to the degree of acetylation. The acetylated dendrimers do not follow the elution behavior of the conventional polymer molecules most probably because of their spherical shape and polycationic nature. This study clarifies the nature of the acetylation reaction and provides a well-defined acylated macromolecule, which can serve as a scaffold for the development of complex dendrimeric structures.