To obtain a monoacylhydrazine, or the like, useful as a synthetic intermediate for diacylhydrazine insecticides by reacting a carboxylic acid (salt) with hydrazine (salt), or the like, in the presence of a triazine substituted with chlorine, or the like.

The objective hydroxytriazine of formula III and (substituted) monoacylhydrazine of formula IV can be produced by reacting a carboxylic acid (salt) of the formula (R1CO2-)nM+n (R1 is H, a 1-8C alkyl or the like; M is H, Na, K or the like; (n) is 1 or 2) with a hydrazine (salt) of formula I (R3 to R5 are each H, a 1-8C alkyl or the like), its hydrate or a substituted hydrazine (salt) or its hydrate in the presence of a triazine substituted with at least one chlorine or fluorine atom and expressed by formula II (X is F or Cl; Y is F, Cl, a 1-4C alkyl or the like).