A process is described for producing alkyl tertiary-alkyl ethers in one step which comprises reacting tertiary-butanol with an alkanol in the presence of a catalyst which exhibits extended life comprising β-zeolite modified with one or more metals selected from groups IA (especially Li) and IIIB (especially rare earth) of the Periodic Table and continuously contacting the alkanol and tertiary-butanol in a molar amount from 1-10:10-1 over the zeolite catalyst at a temperature of 20-250°C and at a pressure of about atmospheric to 1,000 psig.