Reaction of picolinic acid anhydride with dry benzene under Friedl-Crafts conditions gave 3-benzoyl picolinic acid 1 which on reaction with hydrazine hydrate in boiling n- butanol afforded 5-phenylpyrido[3,2-d]pyridazine-8(7H)-one 2. Reaction of pyridazinone 2 with ethyl chloroacetate in dry acetone and K2CO3 gave ethyl 2-( 5-phenylpyrido[3,2- d]pyridazin—8-yloxyl)acetate 3 which on reaction with hydrazine hydrate in refluxing ethanol afforded 2-( 5- phenylpyrido [3,2-d]pyridazin—8-yloxyl)acetohyrazide 4 .Cyclization of the acid hydrazide 4 with phenyl isothiocyante under different conditions afforded oxadiazole and thiadiazole derivatives 9 and 10. Also, cyclization the acid hydrazide 4 with of CS2 in alcoholic KOH and with benzoic acid in refluxing with POCl3 gave oxadiazole derivatives 12 and 13 respectively . Hydrazones 14a,b and c were prepared via the reaction of the acid hydrazide 4 with appropriate aldehydes flowed by treatment with thioglycolic acid gave thiazolidine 15a,b and c, while on reaction of 14a with ethyl chloroacetate flowed by refluxing in dichlorobenzene yielded pyrazole derivative 17. The structure of new compounds was confirmed from its correct analytical and spectral data.