Ono-i-Lau is a group of islands within a barrier reef system in the Fijian archipelago of Lau Islands (ono means "six" in the Fijian language).

There are four central volcanic islands: Onolevu, Doi (or Ndoi) Lovoni and Ndavura, the uppermost parts of the volcanic edifice rising from the Lau Ridge slightly more than 1,000 metres (3,300 feet) below sea level and on which the reef and other islands are built.

The group forms one of the southernmost of the Lau Islands; it is located at 20.80° South and 178.75° West, and occupies an area of 7.9 square kilometres (3.1 square miles).

It is 90 kilometres (56 mi) south-southwest of Vatoa, the nearest largish island; the only land further south in the Lau Group is in the two small Tuvana islands of coral limestone and sand.

The group was the location of the first recorded communication between Fijians and Europeans – Captain William Oliver and men of the Matavy, tender to HMS Pandora, in June 1791.