To obtain a perfectly degradable coated granular fertilizer capable of feeding effective fertilizer components to a plant in the early stage of growth.

A thermoplastic biodegradable resin is melted by heating, this molten resin and a granular fertilizer are stirred and powdery ammoniacal nitrogen is added to them under stirring. The surface of the granular fertilizer 1 coated with the biodegradable resin 2 is coated with a degradable coating film contg. the ammoniacal nitrogen 3 and the objective perfectly degradable coated granular fertilizer is produced.