Alkoxyallylthiopyridazine derivatives which exhibit superior effect for the treatment of hepatic diseases were synthesized from maleic anhydrides. The reaction of maleic anhydrides with hydrazine monohydrate in aq HCl at reflux afforded dihydroxypyridazines, which were transformed to dichloropyridazines with phosphorus oxychloride. The substitution of the first chlorine atom in dichloropyridazines proceeded selectively with alcoholic sodium alkoxides in THF to afford alkoxychloropyridazines, which were converted to alkoxyallylthiopyridazines with lithium 2-propene-1-thiolate in high yields.