Abstract: A process for producing methyl tertiary butyl ether is disclosed, comprising reacting isobutylene and methanol using a hydrocarbon mixture of 4 carbon atoms containing isobutylene and methanol as starting materials in a reaction zone containing an acidic ion exchange resin and distilling the resulting reaction mixture in a distillation column connected to the reaction zone to separate methyl tertiary butyl ether from the unreacted hydrocarbon mixture of 4 carbon atoms, wherein a mixture of the hydrocarbon mixture of 4 carbon atoms as a distillate from a top of the distillation column and methanol as a distillate by azeotropy is contacted with water in a second extraction step to wash and extract methanol with water, and the water containing the extracted methanol is then contacted with said hdyrocarbon mixture of 4 carbon atoms containing isobutylene which is fed to the reaction zone in a first extraction step in an upstream of the reaction zone to thereby transfer a part or a large portion of the methanol in