Abstract: A thin layer chromatography-flame ionization detection (TLC-FID) technique was introduced in this paper to predict the viscosity of heavy oil in reservoir. The new method was convenient, efficient and economic. It took 3 steps. First, representative heavy oil samples were collected from oilfield, and the relative mass-to-area responses of aliphatic, aromatic, resin and asphaltene fractions of oil were determined respectively through preparing the fractions with column liquid chromatograph. Second, TLC-FID analysis and viscosity test of a certain amount of heavy oil samples were carried out, establishing an exponent mathematical relationship between them. Finally, viscosity of the to-be-predicted heavy oil could be calculated with TLC-FID data of the extract of oil sand according to above relationship. The method was practiced to establish viscosity profile of single well in an oil production area of China through analyzing 27 heavy oils from the area and 152 extracts of oil sands from the well, and the result achieved was reasonable.