The t-BuOK promoted stereoselective isomerization of allylarylethers has been developed. The reactions proceeded well in methyl tert-butyl ether (MTBE), providing the corresponding products in good to excellent yields (83–96%). Most of the substrates were isomerized predominantly to the Z isomers with excellent stereoselectivities. Gram-scale synthesis was also achieved on a 10 mmol scale. Moreover