Grynchae or Grynchai () was a town of ancient Euboea. Probably it is identifiable with the place-names that Stephanus of Byzantium mentions under the variants Rhyncae or Rhynkai (᾿áÃÂóúñù) and Trychae or Trychai (äÃÂÃÂÃÂñù). It belonged to the Delian League since it appears in the tribute lists of Athens between the years 451/0 BCE and 416/5 BCE, where it paid a phoros of 1000 drachmae. At the end of the 5th century BCE, it became a deme of Eretria.
Its site is located near modern Krieza.