Pyridazine thione 1 was used as a key intermediate for the preparation of numerous pyridazine derivatives. Reaction of 1 with copper bronze, nitrous acid, anthranilic acid, acetylacetone and benzalacetophenone afforded the bis pyridazine, quinazolinone, diketo and the adduct derivatives. Condensation of the diketo and the adduct derivatives with hydrazine hydrate gave the corresponding pyrazole and hydrazone derivatives. The behaviour of 1 towards thiourea, ethyl chloroacetate and aromatic amines has also been studied. The reaction of the resulting products with diethyl malonate/acetyl chloride, aromatic amines, sodium hydroxide and hydrazine hydrate has also been taken into consideration. The antitumor activity of some of the synthesized compounds were tested