A process is disclosed for the highly selective skeletal isomerization of linear olefin-containing organic feeds to iso-olefins at high levels of feed conversion wherein linear olefins, e.g., n-butenes, are contacted with catalyst comprising ZSM-22 having a crystal size whose largest dimension is no greater than 0.5 micron. The process is carried out under isomerization conditions to produce iso-olefins of corresponding carbon number, e.g., isobutene. High overall iso-olefin yields thus can be obtained, even at relatively low temperatures.