陰陽石, Sacred rock formation in Kobayashi, Japan.

The Yin-Yang Stone is a pair of natural rock formations in the Iwase River in eastern Kobayashi, Miyazaki Prefecture. The larger is a 17.5-meter-high phallic rock called the male stone; beside it lies a female stone with a circumference of 5.5 meters. Both were shaped by erosion of deposits from the Kakuto pyroclastic flow.

The rocks were shaped by erosion of deposits from the Kakuto pyroclastic flow, produced by a major eruption about 330,000 years ago. They became widely known only after a new road was built in 1917; before that, visitors reached them by footpath. In 1950 the city opened the Hamanose-so inn, and in 2009 the prefecture designated the site a natural heritage under the theme "birthplace of life."

The two rocks are venerated as a married couple, and people come to pray for matchmaking, conception and safe childbirth. A local legend says a dragon ascending to heaven paused, struck by the beauty of a woman. Since 1917 a new road has brought visitors, and a festival is held here every year on the autumnal equinox, 23 September.

The stones stand in the Iwase River at Sannomiya Gorge, downstream in eastern Kobayashi; the riverbank is reached by road, and the site has no marked mountain trail. Hamanose-so, a Kobayashi city facility, opened beside the river in 1950. The riverbed is uneven, so wear shoes that can get wet.

The pair was designated a Miyazaki Prefecture Natural Heritage site in 2009 under the theme "Sacred Ground of the Origin of Life," on the proposal of then-governor Hideo Higashikokubaru. The citation stressed the size of the rocks and the rare fact that both a male and a female stone stand together.