Five species of molluscan borers belonging to families Teredinidae and Pholadidae were found infesting the mangrove plants of Karachi. Synonyms and differentiating characteristics of the following five species are presented and pallets and shells illustrated: Bankia rochi, B. campanellata, Dicyathifer manni, Lyrodus pedicellatus and Martesia striata. These are reported for the first time from Pakistan. No relation between size of wood and number of borers was found. In most cases, wood contained individuals of one species. However, occurrence of 2 or 3 species in the same wood was not uncommon. D. manni and B. rochi are large size species which may grow over 24.0 cm in body length, whereas L. pedicellatus is a small size species. Recruitment of L. pedicellatus continued throughout the year. Although B. rochi showed year round recruitment in Sandspit, it occurred twice a year in Port Qasim area. No infestation of borers was found in Clifton mangroves.