This article describes studies on the catalytic activity of several nitrogen-based organic catalysts for the depolymerization of poly(ethylene terephthalate) (PET), in which a few cyclic amidines work more effectively than a potent, bifunctional guanidine-based catalyst 1,5,7-triazabicyclo-[4,4,0]dec-5-ene (TBD) in the presence of short chain diols that play a role in activation of carbonyl groups through hydrogen bonding. Further studies prove that the catalytic efficiency at the above specific conditions depends only on the extent of activa-tion of a hydroxyl group rather than simply the pK a of the bases. For glycolysis with excess short-chain alkanediols, 1,8diazabicyclo[5.4.0]undec-7-ene is the best catalyst. In contrast, TBD shows outstanding catalytic activity in depolymerizations of PET with mono-alcohols and longer-chain diols.