In this paper, we studied olefin homologation reactions on zeolite ZSM-22, whose one dimensional pore structure inhibited the hydrocarbon pool mechanism and secondary reactions of the methanol to olefin (MTO) conversion. Homologation of ethylene, propylene and styrene were directly observed between C-13 labeled methanol and olefins. isotopic tracking shows high selectivity for homologation reaction, e.g. from ethylene, propene has one C-13 atom, butene has two C-13 atoms, and pentene has three C-13 atoms. Homologation of styrene's side chain also showed very specific isotopic pattern. The role of olefin homologation is speculated as a key reaction during the induction time of MTO process. (C) 2008 Elsevier Inc. All rights reserved.