NOx reduction in diesel exhaust using selective catalytic reduction by methanol over alumina catalyst was investigated. Although a slight decrease in catalytic activity took place at the initial stage of the catalyst evaluation, more than 40% NOx conversion was obtained at 400 degrees C and a space velocity of 10 000 h(-1) by using a ball type alumina catalyst and methanol (CH3OH/NOx mole ratio = 2) as a reducing agent. The experimental results using synthetic exhaust gases containing SO2 indicated that the initial catalytic deactivation is ascribed to the formation of Al-2(SO4)(3)-like species on alumina surface through reaction with SO2. However, the formation stopped at a certain point in time. The stable activity following the initial deactivation did not depend on SO2 concentration. A durability test of a honeycomb type alumina was also conducted, and more than 70% of NOx conversion maintained for more than 4000 h at a CH3OH/NOx mole ratio of 6. In this case a gradual decrease in the activity of alumina occurred due to catalyst sintering.