A catalytic process is provided for converting lower monohydric alcohols and their ethers, especially methanol and dimethyl ether, to a hydrocarbon mixture rich in C2 -C3 olefins, by contact, under conversion conditions, with a catalyst comprising a crystalline aluminosilicate zeolite having a silica to alumina mole ratio of at least about 12, a constraint index, as hereinafter defined, within the