Abstract: The haze in 120BS bright oil was separated by solvent method. The structure and composition of the haze was characterized by average molecular mass, simulated distillation, gas chromatography (GC) and nuclear resonance (13C-NMR). The results show that the haze does not affect the properties of the bright oil, but affect its appearance seriously, although the content of haze is 0.05% only. The haze is characterized by its higher average molecular mass and higher simulated distillation temperature than the de-hazed oil and is mainly composed of n-alkanes, iso-paraffins, and cycloalkanes. Among of them, 20.2% is high carbon n-alkanes and the rest is i-paraffins and cycloalkanes with lower levels of isomers. All these components have higher freezing point. However, there are some n-alkanes and cycloalkanes with somewhat lower freezing point and low level isomerization in the haze. At the industry level, the haze is actually considered to be composed of a mixture of microcrystal wax and foots oil.