Abstract: Cis- and trans-1,3-dichloropropenes and their homologs and 1,3-dibromopropenes can be prepared by isomerizing the corresponding 3,3-dihalopropene or homolog thereof in a simple, high yield process by contacting the latter with an effective silica, alumina, or zeolite catalyst. Thus, a mixture of cis- and trans-1,3-dichloropropenes is produced in good yield and with good selectivity when a mixture of 3,3-dichloropropene with other chlorinated hydrocarbons, principally 1,2-dichloropropane, is contacted with an acidic activated alumina catalyst at a temperature of about 100.degree. C.