Two barnacle species (Semibalanus cariosus and Chthamalus challengeri) were studied during two years at Hokkaido, northern Japan, to find the interspecies boundary and to determine whether interspecific competition (interference and pre-emption) is important in maintaining the zonation in our study system. Both barnacle species showed tide level dependent distribution patterns in the boundary zone. Semibalanus cariosus was dominant at lower levels; this pattern was determined by post-recruitment mortality. This mortality pattern seemed to be set by physical stress because recruitment density and survival rate were not correlated with the cover of other species, and mortality was higher in higher zones where physical stress is more severe. Chthamalus challengeri was dominant at higher levels; this pattern was determined by recruitment. The recruitment density and survival rate of this species were not affected by the covers of other species, thus, neither interference nor pre-emption significantly affected the distribution pattern. Interspecific competition appears to be less important in organizing barnacle communities in our study area than in previously studied areas, however, the recruitment process is of major importance.