PURPOSE: To reduce the amount of steam to be used and to obtain hydrazine in an advantageous manner by adding a hydrating agent to an aqueous hydrazine soln. obtd. by bringing NH3 and an aqueous slkali hypochlorite soln. into a reaction and by removing produced solid hydrate.

CONSTITUTION: An aqueous NaOCl soln. and a large excess of NH3 are brought into a reaction with steam as a heat source to obtain a dil. aqueous hydrazine soln. having about 2wt% concn. After purging the residual NH3 from the hydrazine soln., a hydrating agent capable of producing soild hydrate with water such as CCl2FH is added to the hydrazine soln. to convert a considerable amount of water in the soln. into solid hydrate, and an aqueous hydrazine soln. concd. to 5W6% is obtd. by removing the solid hydrate. NaCl deposited in the hydrazine soln. is removed, and the soln. is concd. by a known method to obtain hydrazine. The amount of steam required to manufacture hydrazine can be considerably reduced as compared to a conventional method.