Ua Pu (French: Ua Pou, North Marquesan: ’uapou) is the third largest of the Marquesas Islands, in French Polynesia, an overseas territory of France in the Pacific Ocean. It is located about 50 km (30 mi.) south of Nuku Hiva, in the northern Marquesas. Until the beginning of the 1980s, it was the most populous of the Marquesas Islands, because when the other islands were being ravaged by diseases introduced by European explorers and traders, the Catholic priests on the island finally took to quarantining the remnant of the native population inside their churches whenever visiting ships approached the island, thereby reducing their exposure to external diseases.
The center of the island is characterized by four high basalt pillars that reach high above the surrounding mountains. The highest of these pillars, Mount Oave (French: Mont Oave), reaches to 1,230 m (4,035 ft.) above sea level and is the highest elevation in the Marquesas.
The island covers an area of 106 km (41 sq. mi.), and is located just northwest of the small island of Motu ‘Oa. The population in 2007 was 2,157. The largest settlement is Hakahau, on Hakahau Bay, on the northeast coast.