Transient temperature and concentration distribution inside a catalytic converter during warm-up have been analyzed by experiments and numerical simulation. There is great maldistribution of species concentrations inside a converter during warm-up. Carbon monoxide (CO) and hydrocarbons (HC) have high concentrations in the exhaust gas passing through outer region cells because they are not converted due to low wall temperature.The effects of the noble metal loading pattern on conversion characteristics during warm-up have been investigated by numerical simulation. The effects of high-loading on improving conversion characteristics are saturated with the loading quantity of six times that of the base-loading. High-loading of the noble metal only on the frontal region (20 or 30mm. from the front face) has almost the same warming-up conversion performance as the uniform high-loading.Finally, a new loading pattern that improves conversion characteristics is suggested based on the above results. The quantity of noble metal loaded was six times on the outer region of frontal part, the same on the inner region of frontal part and one-half on the rest as that of the base-loading. This catalytic converter has the same total amount of noble metal loading as the uniform base-loading and shows higher conversion efficiency during warm-up.