A process for producing purified monoammonium phosphate (abbreviated to MAP) directly from wet process phosphoric acid with a high yield is provided, which process comprises reacting wet process phosphoric acid with NH.sub.3 at 50.degree..about.80.degree. C. while keeping the molar ratio of NH.sub.3 /H.sub.3 PO.sub.4 at 0.9.about.1.35; separating the resulting slurry containing MAP crystals and an insoluble sludge into a slurry containing the former and a slurry containing the latter; treating the former slurry in a conventional manner to recover MAP; while treating the latter slurry by heating it to 60.degree..about.95.degree. C. to dissolve MAP contained therein, removing the sludge by centrifugal separation and concentrating the filtrate to recover MAP; and combining the two portions of MAP.