A series of new alkylselenoallylthiopyridazine 12~18 was synthesized as expected to retain anticancer activity. Synthetic route for the final compounds 12~18 was proceeded with diselenylation, hydrolysis/alkylation and allylthiolation from 3,6-dichloropyridazine 1. Dichloropyridazinyl diselenide 2 was prepared from the diselenide anion using synthetic route of Bhasin. Diselenide 2 can be reduced to 3-chloropyridazinyl selenolate anion using hydrazine hydrate at rt in the presence of NaOH in THF. The anion thus formed reacts readily with alkyl halide to give the 3-alkylseleno-6-chloropyridazine 3~11. 3-Alkylseleno-6-allylthiopyridazines 12~18 were prepared from 3~11 with allylmercaptan and sodium methoxide.