Prime Minister Peter O'Neill met with ADB director for PNG, Won-Mok Choi and PNG's Works Minister Francis Awesa in Port Moresby to thrash out the detail.
Full details would be announced in the coming days, O'Neill said.
"We are upgrading the Highlands Highway to international standard, and we are implementing strategies to deal with extreme weather that causes damage.
"Work is already scheduled to begin on crucial parts of the Highlands Highway in the coming weeks, and this will further contribute to long-term positive outcomes for the highway," O'Neill said.
further announcements will be made at the appropriate time.
"As the ADB celebrates its 50th year of operation, I expect that its partnership with Papua New Guinea, and other Pacific nations, will continue to strengthen long into the future."