There are many reports worldwide, which show apparent zonal plant distribution on coastal dunes. In this paper we studied several plants found on many Japanese coastal dunes. Calystegia soldanella (Sea Bindweed) and Elymus mollis are distributed on seaward sites where soil-water salinity is around 100 mM NaCl, whereas Ischaemum anthephoroides is found only on inland sand ridges with about 10 mM NaCl. Carex kobomugi (Sea Isle) and Wedelia prostrata are distributed on foredune sites with 20 -30 mM NaCl. Seedlings of these five coastal sand dune plants were cultivated hydroponically with three NaCl solutions (0, 10 and 100 mM) in a growth chamber. Independent of the salinity levels, Calystegia soldanella and Elymus mollis had the highest relative growth rate (RGR), followed by Carex kobomugi and Wedelia prostrata , and Ischaemum anthephoroides had the lowest. For instance, the RGR values at 100 mM NaCl were 0.085, 0.082, 0.066, 0.065 and 0.060 g/g/d, respectively. The order of RGR coincides with the trend of zonal distribution of the five species. In addition, the overall trends of RGR against the NaCl treatment were primarily determined by those of leaf area ratio (LAR), one component of RGR related to dry matter allocation of a plant. The differences of RGR values among the three species and/or among the salinity levels treated were governed by the LAR . On the other hand, net assimilation rate (NAR), another component of RGR related to photosynthetic activity of a single leaf, was influenced species-specifically by the salinity treatment; a higher level of salinity considerably depressed NAR in Ischaemum anthephoroides, but promoted the NAR in Calystegia soldanella and Wedelia prostrata.