Molluscs (oysters and gastropods) of the Late Paleocene Chehel-Kaman Formation, Kopet-Dagh Basin, NE Iran were significantly colonized by sclerobionts. The largest area of the shells studied is covered by various borings. The diversity of macro-bioeroding ichnotaxa is rather high, including Gastrochaenolites Leymerie, 1842; Maeandropolydora Voigt, 1965; Trypanites Magdefrau, 1932; Talpina von Hagenow, 1840, and possibly Entobia Bronn, 1837. Some slightly conical borings penetrating the shells could belong to predatory tracemakers of Oichnus Bromley, 1981. Encrusters include calcareous polychaetes, cyclostome and cheilostome bryozoans, foraminifera and oysters. Calcareous sabellids [i.e. Glomerula serpentina (Goldfuss, 1831)] and serpulids are equally common sclerobionts in the association. Bryozoans cover a slightly larger area of the substrate than the calcareous polychaetes, while encrusting oysters are subordinate. The majority of fossils in the hard-substrate community studied belong to suspension feeders. Sclerobionts are typical of the shallow-marine environment, commonly in warm water. The present study is the first attempt to record the occurrence and diversity of epi- and endobionts in the organic substrates, present in the topmost part of the Late Paleocene Chehel-Kaman Formation, Kopet-Dagh Basin, NE Iran.