The coking and regeneration of Ni/y-Al2O3 for the cracking of toluene as a tat model compound were investigated. Special attention has been paid on the effect of coke nature, especially filamentous coke, on the regeneration performance. The catalyst was deactivated by cracking toluene at 700 degrees C for 0.5 h. The deactivated catalyst was then regenerated by calcination in air at 600 degrees C for 3 h. The cracking regeneration cycle usage was carried out up to four times. The results showed that the toluene conversion decreased slowly from 28.2% by fresh catalyst to 22.6% by the third regenerated catalyst and then decreased quickly to 16.3% by the fourth regenerated catalyst. The increase of NiO crystal size from 12.8 to 18:0 nm and the decrease of Brunauer-Emmett-Teller (BET) surface area from 97.7 to 86.9 m(2)/g caused by sintering and remaining coke were the major reasons for the loss of catalytic activity of Ni catalyst after cycle usage. The cycle usage made the deposited coke more graphitized by slightly enhancing the formation of filamentous coke but reduced the total quantity of coke. The existence of filamentous coke required a higher regeneration temperature (600 degrees C) due to a more graphitized nature than amorphous coke. The formation and the growth of filamentous coke decreased the Ni particle size from 13.0 nin at 10 min to 11.4 run at 30 min in the fresh cycle and weakened the interaction between metal and support.