The concept to immobilize homogeneous catalyst to a solid support has received considerable attention, as it simplifies the separation of catalyst from products and also it solves the loss of expensive metal complexes such as rhodium in the separation area. Since a rhodium carbonyl iodide complex as a methanol carbonylation catalyst is an anion, the ionic bond immobilization to a pyridinium cation resin support was studied. Virtually all rhodium was immobilized, because the ion exchange equilibrium is understood to favor extremely the pyridinium cation resin. The reaction mechanism was exactly the same as that by homogeneous catalyst and the activity per rhodium was rather increased equivalent to that promoted by addition of iodide additives under low water condition. Therefore, the rhodium complex anion is ionically immobilized as the same formula in the liquid phase and also promoted with surrounding pyridinium iodide back bones. Reaction time or catalyst concentration did not directly affect the rhodium leaching, but the water concentration of the product controlled the rhodium leaching through iodide anions to be exchanged with rhodium complex anions. The catalyst stability for 2,000 hours operation was confirmed using CSTR and no rhodium leaching was demonstrated with 0.3 wt-ppm of co-feed of equilibrium rhodium concentration.