A newly-developed time resolved exhaust gas analysis system was utilized in this study. The hydrocarbon compositions upstream and downstream of the catalytic converter were investigated during cold start and warm up of the Federal Test Procedure(FTP), with three fuels of different aromatic contents.Although engine-out hydrocarbon emissions had high concentrations right after cold start, the specific reactivity was low. This can be explained by the selective adsorption of the high boiling point components which had a high Maximum Incremental Reactivity (MIR) in the intake manifold and engine-oil films. Thereafter, the high boiling point components were desorbed rapidly and consequently specific reactivity increased. Hydrocarbon adsorption of high boiling point components and hydrocarbon conversion of low boiling point components occurred simultaneously on the catalyst during warm up. Although tailpipe hydrocarbon emissions with high aromatic fuel were higher than other fuels during warm up and the specific reactivity increased slightly, because more of the high boiling point hydrocarbon components were adsorbed on the catalyst.On the basis of these characteristics, it has been clarified that hydrocarbon compositions and their specific reactivity are affected by fuel components and change with elapsed time during cold start and warm up of FTP.