Thin wall substrates are requested by automobile companies to obtain lower back pressure and to provide lighter materials than conventional cordierite substrates.Cell strength was increased in thin wall substrates and, as a result, pore volume of the substrates was drastically decreased. Therefore, coatability of thin wall substrates is much worse than that of normal water absorption substrates. To improve the poor coatability, slurry properties of washcoat and coating machines are improved. Catalysts of thin wall substrates have been produced on a commercial scale since 1987. The process coating experiences during this period are discussed in terms of coatability, catalyst physical properties, and catalytic performance in this paper.