Growth of the bivalve-feeder Halla okudai (Polychaeta: Lysaretidae) was evaluated in relation to species and abundance of prey under wild and rearing conditions. The field survey was conducted from May to July 1995 at the M. L. W. S. in 11 intertidal sandy flats of Hiroshima Bay, the Seto Inland Sea. H. okudai habitats were classified into four types by major prey organisms: clam, clam & oyster, oyster, and mussel. The condition factor was highest in the clam & oyster-type habitat with the highest density of Ruditapes philippinarum. The condition factor also increased with increasing the density of R. philippinarum, whereas this was not seen in Crassostrea gigas and Mytilus galloprovinciallis. In laboratory experiment, the growth efficiency was significantly higher in the R. philippinarum-group than in the M. galloprovinciallis- and the C. gigas-groups. Thus, H. okudai is suggested to select prey to maximize the growth.