The intrinsic kinetics for the liquid-phase cyclisation etherification of 1,4-butanediol (BD) to tetrahydrofuran (THF) and water were determined in a stirred batch reactor in the temperature range from 373 to 393 K. A sulphonic acid ion exchange resin powder with a particle size of 3-7 mum was manufactured and used as catalyst. The reaction can be regarded as irreversible and proceeds without diffusion limitations inside the catalytic microspheres. The formation of an intermediate containing 1,4-butanediol (BD) an an active site was determined to be the rate-determining step. The reaction product water acts as a strong inhibitor for the intermediate formation. The experimental results can be described by a three-parameter model based on MichaeIis-hienten kinetics er;tended by an inhibition term for water. Within the developed rate equation. concentrations are expressed in liquid-phase activities from the UNIQUAC method in order to consider the nonidealities. The developed rate equation is valid in the whole range of possible concentrations and independent of the solvents used. During the experiments no formation of by-products was observed.