Hydrodenitrogenation (HDN) of isoquinoline (IQ) over Ni and Pd/C were investigated at 200 and 300 degrees C under pressurized hydrogen. The results show that Ni is less active at 200 degrees C but more active at 300 degrees C than Pd/C for HDN of IQ. Raising reaction temperature from 200 to 300 degrees C significantly increased nitrogen removal selectivity. pi-Electrondensity of pyridine ring and cleavage of C-N bond were investigated and found to play important roles in HDN of IQ.