Tokyo intends to announce more than 40 billion yen (US$355 million; Ђ276.24 million) in aid at the conference, local media reported. The gesture is seen as a way of countering growing Chinese influence in a region Japan considers its own backyard.
Just last month, Chinese Premier Wen Jiabao jetted to the South Pacific to lavish millions of dollars on such countries such as Fiji, Vanuatu and Papua New Guinea.
China uses the aid to shore up local support for Beijing over the island of Taiwan - rivals who split amid civil war in 1949. China considers self-ruled Taiwan to be Chinese territory, and demands that other countries refuse to recognize Taiwan's government.
More widely, friendships with the Pacific nations are also a way for other governments to rack up votes and backing at international venues like the United Nations, the AP reports.
Environmentalists have accused Japan of using Pacific economic aid to buy pro-whaling votes at the International Whaling Commission, a charge Japan denies.
Leaders from the region gathered Thursday night at a banquet in Tokyo and were scheduled to fly to the southern Japanese island of Okinawa for a two-day conference starting Friday. The tropical setting is one way Japan can show it's part of the club.
Invitees are the 16 members of the Pacific Islands Forum, a group founded in 1971. The body, with a secretariat based in Fiji, consists of Australia, New Zealand, Fiji, the Cook Islands, the Federated States of Micronesia, Kiribati, Nauru, Niue, Palau, Papua New Guinea, the Marshall Islands, Samoa, the Solomon Islands, Tonga, Tuvalu and Vanuatu.
Australian Foreign Minister Alexander Downer was expected to attend, but canceled his plans due to violence in East Timor, Japan's Foreign Ministry said Thursday.
Tokyo has hosted a summit every three years since 1997 as a way of reinforcing ties with the region, Kyodo News agency said.