Three species of the family Processidae, Hayashidonus japonicus (De Haan, 1844), Processa sulcata Hayashi, 1975 and Processa zostericola Hayashi, 1975 described with illustrations from Korea. Two of these species, H. japonicus and P. zostericola, represent new records for the Korean carcinological fauna. The genus Hayashidonus included the single species, H. japonicus is distinguished from other genera of Processidae by the broadly triangular rostrum, the obscure or absent dorsolateral spines of the telson, and the exceptionally long molar process of the mandible. Two species of the genus Processa, P. zostericola and P. sulcata are distinguishable each other by presence or absence of an obtuse process of the basicerite of antenna on the anteroventral margin. The basicerite of antenna arms with the obtuse process in P. zostericola, while in P. sulcata the basicerite of antenna lacks the process but is smooth on the ventral margin. A key to these species is presented.