Pyridazine and its 3-oxo derivatives (pyridazin-3(2H)-ones) are one of the most representative classes of nitrogen heterocyclic compounds. A literature overview of the chemistry of 1,2-diazines have reviewed many practical applications, especially in the fields of medicine, opto-electronics and agriculture, and also as building-blocks for other organic/inorganic structures (complexes, macrocycles, etc)1-2 . Acoording to a greate number of recent publications, substituted pyridazinones have received much attention due to their prominent potential as anti-inflammatory & analgesics3 , antiplatelet4 , antihypertensive & antidepressant5 , antitubercular6 , etc. In this research, our main objective was the synthesis of some new 3(2H)-pyridazinoneacetohydrazides starting from their corresponding esters, by adapting the procedure described in literature.figureScheme 1. Synthesis of 3(2H)-pyridazinone-acetohydrazidesfigureScheme 2. Conformational equilibrium between two conformers The structures of newly compounds obtained were proved by spectral analysis (1H-NMR, 13CNMR, IR, MS). According to NMR spectra, the unitary compounds exist at room temperature as a mixture of two conformers. In order to establish the report between the two conformers, and also their stability, some 1H-NMR studies at different temperatures were done. Also, it has been proven that the report between the two conformers is different, depending on the nature of the corresponding ester. The exact ratio of two conformers was determined from 1H-NMR spectra.