Selective catalytic reduction (SCR) of NOx by ethylene was investigated on copper and/or cerium ion-exchanged Al-MCM-41 in the presence of excess oxygen. Ce-Al-MCM-41 showed little activity, but Cu-Al-MCM-41 and cerium-promoted Cu-Al-MCM-41(i.e., Ce-Cu-Al-MCM-41) were found to be active in this reaction. Higher NOx conversions to N-2 were obtained on Ce-Cu-Al-MCM-41 as compared with Cu-Al-MCM-41. The maximum activity of Ce-Cu-Al-MCM-41 was close to that of Cu-ZSM-5, but the former had a wider temperature window. TPR results indicated that only isolated Cu2+ and Cu+ ions were detected in the Cu2+-exchanged Al-MCM-41 samples, which may play an important role in the selective catalytic reduction of NOx to N-2. After some cerium ions were introduced into Cu-Al-MCM-41, CU2+ in the molecular sieve became more easily reducible by H-2. This may be related to the Increase of catalytic activity of NOx reduction by ethylene.