In a process for producing a solid koji for a fermented food product which comprises inoculating a koji mold in a modified koji substrate and cultivating it at a temperature of about 20.degree. C. to about 40.degree. C. for a time sufficient to produce a solid koji for fermented food products, the improvement wherein at a certain time during a period of about 10 hours to about 20 hours after the inoculation of the koji mold, the cultivation system is subjected to a drying treatment to adjust its water content to about 30.+-.5%.