Ōnuma Quasi-National Park (大沼国定公園, Ōnuma Kokutei Kōen) is a 90.83 km (35.07 sq mi) quasi-national park on the Oshima Peninsula in southwest Hokkaidō, Japan. The park encompasses the volcanic Hokkaidō Komagatake (北海道駒ケ岳, Hokkaidō Koma-ga-take) as well as the Ōnuma (大沼) and Konuma (小沼) ponds, which abut against the west slope of the mountain. The park, which was designated as quasi-national in 1958, is the smallest major park in Hokkaidō.

Ōnuma and Konuma were created when mudflows due to eruptions of Hokkaidō Koma-ga-take dammed up depressions at the base of the mountain. The ponds, which are dotted with watershields, are surrounded by birch and maple forests.

• Nanae, Hokkaidō

• List of national parks of Japan

• J-IBIS (in Japanese)