A bark beetle Coccotrypes gedeanus Eggers (Coleoptera: Curculionidae: Scolytinae) is a dominant insect seed predator of dipterocarp fruits in the lowland tropical rainforests of Southeast Asia. In this study, the host preference and host range of C. gedeanus was determined by sampling 22,216 fruits from 137 species of 59 genera belonging to 24 families in a primary lowland mixed dipterocarp forest in Borneo. Coccotrypes gedeanus adults were found in the fruits of 51 species from 19 genera belonging to 13 families, and were observed to settle in the fruits of 34 species of 11 genera belonging to 6 families to initiate breeding. Except one plant species, the rest of the 34 plant species were confirmed to bear “nut” or “drupe” type fruit. These results suggested that a population of C. gedeanus utilize seeds of various plant species simultaneously. The polyphagy of the bark beetle might be adaptive for survival in the Bornean tropical rain forests where the density of each plant species is low, and most plants produce fruits at unpredictably long intervals. Our results also suggested that the characteristics of fruit might affect the host plant preference of C. gedeanus adults and/or the growth performance of C. gedeanus larvae.