Abstract: The products of hydrotreated animal fats or vegetable oils were analyzed by IR spectrometer. The corrected height of the peaks at 2 925, 1 745, 1 710 cm-1 were used to calculate A1745/ A2925, a ratio of ester to alkane and A1710/ A2925 , a ratio of acid to alkane, which represent the contents of ester and acid in product, respectively. The results show that A1745/ A2925 and A1710/ A2925 are very effective to differentiate the hydrotreating depth, and can be used to screen the suitable reaction conditions for animal fats or vegetable oils hydrotreating processes.