To provide a method of producing carbodihydrazide of high purity in high yield from an inexpensive and easily handleable starting substance under mild reaction conditions as a starting substance is recycled.

Hydrazine hydrate and propylene carbonate are allowed to react with each other under mild conditions to synthesize the objective carbodihydrazide and the product is isolated. The hydrated hydrazine and propylene glycol in the separated mother liquor are recovered by distillation. The propylene glycol is allowed to react with urea to convert to propylene carbonate, then the recovered hydrazine hydrate and the propylene carbonate are recycled to the reaction system.