The factors affecting the age of olefin skeletal isomerization catalyst are investigated. Molecular sieves with different acid strength and distribution show different activity and stability. Weak and moderate acid centers are responsible for the skeletal isomerization of olefin (SIO) and strong acid sites catalyze dimerization and cracking reaction under the test conditions. The pore structure of molecular sieve influences the products distribution significantly in the skeletal isomerization of 1-hexene. Choosing suitable modification methods to diminish external surface acid center could reduce the influence of external surface coke on molecular sieve activity. Under the same olefin saturation level, the octane loss of light FCC naphtha decreases remarkably by SIO comparing with direct hydrogenation. (C) 2003 Elsevier Science B.V. All rights reserved.