Cordierite honeycomb with hexagonal shaped open channels was formed by extrusion forming technique using specially designed mould for the raw oxide mixture of talc, kaolin, alumina and aluminum hydroxide. The honeycomb showed extremely thin wall thickness of 0.15 mm and low coefficient of thermal expansion (CTE) for the high number of cells per square inch (cpsi) approaching to 600. The extruded honeycomb was sintered at various conditions and characterized by XRF, TGA-DTA, XRD, TMA and SEM techniques. The indialite crystalline showing the coefficient of thermal expansion of 1.9 × 10-6/°C was formed while sintering at 1,450°C for 5 h. The influence of Fe2O3 additive and heating condition on the CTE of cordierite was analyzed in details. This particular cordierite honeycomb with high numbers of hexagonal shaped open cells showed a distinct advantage of saving the amount of precious metal catalyst materials to be coated on the substrate in comparison with the honeycomb with rectangular cells while improving the degree of catalyst efficiency when applying the substrate of automotive catalytic converter.