Abstract: The kinetics of octamethylcyclotetrasiloxane ring-opening polymerization in microemulsion with pentanol as co-emulsifier and dodecylbenzene sulfonic acid as emulsifier as well as catalyst were studied.The effects of reaction temperature，ratio of emulsifier-to-coemulsifier and introducing crosslink agent VTMS on polymerization rate were investigated in detail.The results showed that microemulsion polymerization did not have any constant reaction rate period as was observed in conventional emulsion polymerization.The polymerization reaction rate increased immediately,entering a fast reaction stage then decreased quickly after reaching a certain conversion,and finally approached equilibrium conversion.A higher temperature was favorable to speeding up polymerization.The size of initial monomer drops became smaller with increasing ratio of emulsifier-to-coemulsifier.This speeded up polymerization and decreased the size of polymer latex particles.Introducing crosslink agent VTMS could change linear polysiloxane into crosslinked elastic network and influence the equilibrium of the condensation reaction of end-hydroxyl polysiloxane by inhibiting inverse reaction.The polymerization was speeded up as well.