A tertiary olefin is produced by contacting a gaseous tertiary ether usually represented by the following general formula: ##STR1## wherein R.sup.1, R.sup.2 and R.sup.3 are alkyl groups each having 1-4 carbon atoms which may be same or different and R.sup.4 is an alkyl group having 1-3 carbon atoms, with a catalyst obtained by calcining a silica-alumina compound at 700.degree.-1100.degree. C. in order to effect cracking of the tertiary ether. This reaction may be carried out in the presence of steam to result in further improvements.