The present invention provides a process for producing an aromatic unsaturated compound of the formula (4) ##STR00001## wherein Ar represents an optionally substituted aromatic group or an optionally substituted heteroaromatic group, and Y represents an electron withdrawing group, which comprises reacting (a) a compound of the formula (1) Ar--H (1) wherein Ar has the same meaning as defined above with (b) a compound of the formula (2) ##STR00002## wherein Y has the same meaning as defined above, and Z represents a lower alkoxy, or a compound of the formula (3) ##STR00003## wherein Y and Z have the same meanings as defined above, in the presence of (c) an acid or a compound which generates a mineral acid by its hydrolysis.