It is well known that marine fuels have been getting heavier and lower in viscosity resulting in poorer combustion quality for the last 10 years. In this study, the effect of chemical composition of residual fuels on its ignition and combustion quality was investigated. Residual fuels are mixture products consisting of vacuum residue (VR) and some intermediate products of oil refinery process; straight-run light gas oil (LGO), vacuum gas oil (VGO), FCC light cycle oil (LCO), and FCC clarified oil (CLO). The blend compositions were estimated by thermal and chemical analyses, by using thermogravimetry (TG) and gas chromatography / mass spectroscopy (GC/MS), and discussed with the results of combustion characteristics, by using Fuel Combustion Analyzer (FCA). The fuel ignition quality is significantly affected by the amounts of both 2-ring polycyclic aromatic hydrocarbons and relatively lower molecular weight alkane series (C13-C21), which are interpreted as the amounts of LCO and LGO.