The carbon dioxide reforming of methane over commercial Ni/SiO2-MgO catalyst under periodic and steady state operations was investigated at a temperature range of 650-750 ℃. Under steady state operation, methane conversions tended to be constant with reaction time but increased with increasing reaction temperature. It was then observed that at low temperature (650 ℃) under the periodic operation, methane conversion was also constant at approximately 48% throughout reaction time, but for the operation at a higher temperature, i.e. 750 ℃, higher methane conversion (about 67%) was initially achieved but decreased dramatically with reaction time (to 27% in 240 min). The reason for the catalyst deactivation particularly for the periodic operation was further investigated by TPO, BET and XRD. It is suggested that at different operating temperatures, various types of coke occurred on the surface of catalyst and affected the catalytic activity.