Abstract: Hydroxy terminated polydimethylsiloxane (PDMS)was synthesized by using the one-step process via the anionic ring-opening polymerization of octamethylcyclotetrasiloxane (D₄) catalyzed by tetramethyl ammonium hydroxide (TMAH) in the presence of a minute amount of water.Based on the conversion and molecular weight of synthesized polymer determined with gel permeation chromatography (GPC), the teminated hydroxy group concentration (［OH］) of polymer was calculated. According to the mechanism study of teminated hydroxy formation and the transformation of catalyst in the process of polymerization, a kinetic model of teminated hydroxy formation was established.The relationship between chain transfer rate constant and temperature was obtained from the experimental data.The kinetic behavior of teminated hydroxy formation could be predicted by using the kinetic model.