Abstract: Molecular transformations of heteroatomic compounds during visbreaking of Venezuela Orinoco AR were studied by ultrahigh-resolution negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR MS). The results indicated that the relative abundance of O₂, O₁, N₁O₂, S₁, O₁S₁ and O₂S₁ are decreased or even disappeared, but those of N₁, N₂, N₂O₁, N₂S₁, N₃, N₃O₁, and N₁S₂ are increased after the visbreaking. The highest relative abundance is O₂ class in Venezuela Orinoco AR, while in the visbreaking product (VB) it is N₁. The high abundance O₂ class contains the species with double bond equivalents (rings plus double bonds, named DBE) 3 and 4 in the AR, which are 2 or 3 cyclic naphthenic acids. By visbreaking, the relative abundance of O₂ class is decreased and carbon number is also reduced, mainly DBE 1~4 compounds. The highest abundance N₁ class contains the species with DBE 12 in the AR. After visbreaking, a bimodal DBE distribution around 12 and 15 is observed for the N₁ class, suggesting two possible stable core structures. The distribution of carbon number and highly abundance of carbon number distribution is reduced, suggesting that the side-chain cracking reaction is mainly concerned for N₁ class compounds.