Supported ionic liquid phase (SILP) catalysts have been studied with regard to their long-term stability in the continuous gas-phase hydroformylation of propene. Kinetic data have been acquired by variation of temperature, pressure, syngas composition, substrate concentration, and residence time. The activation energy was determined to be 63.3 +/- 2.1 kJ mol(-1), which is in good agreement with known results from biphasic hydroformylation. The results from the kinetic studies confirmed previously published results on the homogeneous nature of the heterogenised Rh-SILP catalyst. Long-term stability exceeded 200 h time on stream with no loss in selectivity. A small decrease in activity could be compensated by a vacuum procedure regaining the initial activity.