"Myanmar has recently ratified it and will be announcing it next week officially," Singapore's Foreign Minister George Yeo told Dow Jones Newswires in an interview published on the ministry's website www.mfa.gov.sg.
Representatives from ASEAN's 10-member countries will meet in Singapore next week to discuss the early ratification of the charter and the creation of a human rights body.
Often dismissed as a talking shop, ASEAN signed the charter last November with the aim of creating an economically, socially and politically integrated bloc by 2015.
Only Thailand, the Philippines and Indonesia have not ratified the charter, whose soft deadline is in December. Some members of the Philippines senate have threatened to block the ratification of the charter unless Myanmar releases democracy icon Aung San Suu Kyi.
But Yeo said he was confident the charter would be fully ratified by the end of the year.
"I'm not pessimistic about the Philippines, I fully expect that the charter would be fully ratified by the time of the next summit at the end of the year."
ASEAN's members are Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, the Philippines, Singapore, Thailand and Vietnam.
(Reporting by Melanie Lee; Editing by Jan Dahinten)