Provided is a process for producing a wet masterbatch which, without deteriorating a reinforcing property of a rubber composition and rubber physical properties, micronizes a filler slurry by controlling an amount of functional groups on a filler surface, and improves filler dispersibility in the rubber wet masterbatch and the rubber composition. The process for producing a wet masterbatch comprises: a step of producing a slurry solution having a pH of 8 or more by dispersing carbon black having an average amount of surface acidic functional groups (μeq/m2) of 0.15 or more and less than 3.00; a step of producing a mixture by mixing the slurry solution and a rubber latex solution in a liquid phase; and a step of drying the mixture.