The present invention provides an improved process of preparing hydralazine hydrochloride, which involves the preparation of 1-chlorophthalazine salt and further reacting with hydrazine followed by purification of hydralazine hydrochloride, which is free of phosphate, does not contain any individual impurities more than 0.05%, total impurities less than 0.5%, and a hydrazine content of not more than 0.001%, and preferably less than 0.0003%. One benefit of improved purity is enhanced storage stability.