Buergeria japonica is one of a few frogs that breed in coastal areas. To understand why this species can breed in coastal areas, I tested the salinity tolerance of eggs of B. japonica collected from a coastal area of Okinawa Island, Japan. All eggs hatched within four days after oviposition. At 0‰ salinity (control), over 94% of eggs hatched normally, and even at 1‰ salinity over 85% of eggs hatched. Survival rate of eggs was low at 2, 3, and 4‰, and no eggs hatched at 5‰ salinity. These results indicate that low salinity, close to pure water, is necessary for successful egg development, even for populations of B. japonica that breed in coastal areas. Future studies are necessary to examine whether females of B. japonica breeding in coastal areas select appropriate oviposition sites where the environmental salinity level is sufficiently low for eggs.