This study was conducted to compare the species composition of sessile organisms on the artificial substrates of PVC submerged at different time intervals and duration in Jangmok Bay, Geoje Island, southern coast of Korea. Three PVC plates were submerged at one month interval from March to October and retrieved in November, 2007. A mussel, Mytilus galloprovincialis exclusively occupied the artificial substrates submerged from March to April and occurred as a dominant species to July. An ascidian, Styela plicata occurred as a dominant sessile species from May to August. Balanus amphtrite, Bugula sp., and hydrozoans occurred as dominant species on the plates submerged from July to September. There was a mis-match between the peak time of settlement and dominance of sessile organisms due to the interspecies competitions when the PVC plates were retrieved in November. There was no clear relationship between submerged duration and the abundance of sessile organisms due to the different settlement period. M. galloprovincialis seemed to be a strong competitor which could exclude the previous recruiters of macroalgae by overgrowth and occupy the substrate surface and maintain its high population density by preventing the settlement of other species until late autumn. These results suggested that the composition of sessile organisms in vacant hard substrates could be determined by the combined effects of supply-timing of larvae and post-settlement competitions.