Abstract: A process for the preparation of a tertiary alkyl ether, in particular methyl tert. amyl ether (MTAE), is described which comprises reacting, in a reaction section, a charge constituted by a mixture of C.sub.5 hydrocarbons, including reactive isopentenes, with an aliphatic monoalcohol in excess, such as methanol, ethanol, propanol or isopropanol, and collecting in the bottom of a fractionation section the corresponding pure tert. alkyl ether. The head effluent, after condensation, is subdivided into a liquid reflux and a distillate. The process is further characterized by providing a finishing reactor for the reflux, or for the reflux + distillate effluent prior to the subdivision thereof, or two finishing reactors are provided, one for the reflux and the other for the distillate, along with the possibility of injecting aliphatic monoalcohol upstream of each finishing reactor.