Allylthio group of the sulfur compounds of garlic oil plays an important role for prevention and treatment of hepatic diseases induced by toxic substances or carbon tetrachloride. Thus allylthio group as pharmacologically active group was introduced into pyridazine heterocycle ring. Aryloxyallylthiopyridazine derivatives were synthesized and their hepatoprotective activities were screened in rat. The activities of these compounds were weaker than alkoxyallylthiopyridazine derivatives, which exhibit a superior hepatoprotective effect.