To evaluate the thalassochory potential of the coastal dune plant Linaria japonica Miq., the buoyancy and viability of seeds exposed to salt water （3.45% sodium chloride solution） were examined.　The results showed that most seeds continued to float on salt water for more than one month.　In laboratory germination tests under controlled conditions, the final germination rate was significantly lower in seeds exposed to salt water for one month than in control seeds without exposure to salt water.　However, more than 40% of the former seeds germinated.　In sowing tests using pots under outdoor conditions, there was not a significant difference in the final emergence rate between seeds exposed to salt water for two months and control seeds.　These results suggest that L. japonica has thalassochory potential, and its viable seeds can be successfully dispersed over a long distance via sea currents.