Heavy oils are commonly found in China; however, the Karamay heavy oil is unique among all. It has very low asphaltene content and is an excellent feedstock for producing high-quality lubricant base oils. Physical characteristics of the oil are dependent on its chemical composition, which is quite difficult to be characterized due to its complexity. In this work, the bulk properties and molecular composition of the Karamay heavy crude oils were characterized and compared with those of other heavy oils. It was found that the high concentration of compounds with long side chains and low naphthenic skeletons makes the Karamay heavy oil exhibit a high viscosity index. The viscosity of Karamay heavy oil is less temperature dependent at high temperatures, which is technically challenged for using thermal enhanced oil recovery techniques in oil production. However, the chemical composition of Karamay heavy oil is ideal for use as a lubricant base oil. Moreover, the low total sulfur content and high sulfides/thiophenes ratio of Karamay heavy oil provide good oxidation stability. Special biological precursors and geological history were considered to elucidate the unique molecular composition of Karamay heavy oil.