The kinetics of the catalytic hydrogenation of dimethyl itaconate (DMI) was studied in a biphasic cyclohexane-water system and in a [Triton X-100/1-pentanol]/cyclohexane/water microemulsion. in both cases using the water-soluble catalyst complex Rh-TPPTS. The reaction was carried out at a pressure of 1.1 bar and in the temperature range 298-308 K. A typical profile of a zero-order reaction was observed in the case of the biphasic system. Against that the reaction order for DMI changed to 1 in a microemulsion. A rate law based on an Osborn-Wilkinson-like kinetics was used to describe the experimental results which were governed by the irreversible attack of free DMI at the rhodium complex. The activation energy of the rate-determining step is 53 kJ mol(-1) and is similar in both systems.