PURPOSE: To readily obtain the title compound useful as a fuel for automobiles from easily obtainable raw materials by an extremely simple method by blending a mixture of methanol and butanol having a specific composition with a hydrase at a normal temperature while stirring.

CONSTITUTION: A mixture comprising 40-90wt.% methanol and 60-10wt.% butanol is packed into a reactor, 1/1,000-1/500pt.wt. based on 1pt.wt. mixture of a hydrase is added to the reactor, the mixture is blended with the hydrase at normal temperature while stirring and formation of methyl tert-butyl ether as a reaction product is confirmed by gas chromatography. Consequently, the objective tert-butyl ether useful as a fuel for automobile or an antiknock for gasoline is readily produced by using readily obtainable butanol and methanol as raw materials without utilizing isobutylene as a raw material.