Abstract The synthesis of the novel pyrazolo [4′, 3′: 5, 6] pyrido [2, 3-d] pyridazine ring system and some of its derivatives has been accomplished such as 4-amino-1-phenyl-5, 8- dioxo-, 4-amino-5, 8-dioxo-, 1-phenyl-5, 8-dioxo-, 5, 8-dioxo-, 5, 8-dichloro-1-phenyl-, 5- ethoxy-1-phenyl-and 8-ethoxy-1-phenylpyrazolo [4′, 3′: 5, 6] pyrido [2, 3-d] pyrid-azines.