Feeding habits of Rudarius ercodes collected from a Zostera marina bed in Jindong Bay, Korea were studied. R. ercodes was a omnivore which consumed mainly gammarid amphipods, polychaetes and eelgrass, Z. marina. Its diets also included a small amount ofcopepods, urochordates and caprellid amphipods. R. ercodes showed ontogenetic changes in feeding habits. Small individuals less than 2 cm SL fed mainly on copepods, however, gammarid amphipods and polychaetes were heavily selected with increasing fish size. The consumption of eelgrass by R. ercodes was 10-20% all size classes. The dietary breadth of R. ercodes were varied with fish size.