Detailed structural information on sulfur-containing aromatic compounds in heavy oils is valuable for the petroleum industry. In this work, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) combined with collision-induced dissociation (CID) was applied to study the structures of sulfur-containing aromatic compounds in vacuum gas oil (VGO) and vacuum residue (VR). The parent ions of the sulfur-containing model compounds and high-sulfur heavy oils were isolated by the quadrupole in FT-ICR MS with a narrow isolation window of 1 Da. For most of the sulfur-containing model compounds, removal of S atoms was achieved in the collision voltage range 10-30 V. On the other hand, the removal of S atoms from the sulfur-containing compounds in heavy oils was restrained by optimization of the collision voltage. The structures of VGO and VR were also studied by CID FT-ICR MS with a narrow isolation window at the optimal collision voltages. The results suggested that naphtheno-aromatic sulfur-containing compounds were components of heavy oils and that the structural diversity of the heavy oils increased significantly with an increase in molecular weight.