Burma's opposition leader Aung San Suu Kyi is due to take her seat in parliament, a month after her party won a sweeping victory in by-elections.
She and 42 members of the National League for Democracy (NLD) refused to take part in the swearing-in ceremony due to the wording of the oath.
They had objected to swear to "safeguard" the constitution drafted by the old military government and wanted to change the wording to "respect".
But they later agreed to take the oath.
"The reason we accept (the oath), firstly is the desire of the people. Our voters voted for us because they want to see us in parliament," Ms Suu Kyi said.
However, the constitution - which enshrines the armed forces' role in politics - will continue to be the focus of political battles in Burma, reports the BBC's Rachel Harvey in Burma's capital Nay Pyi Taw.
Ms Suu Kyi's parliament debut comes after a recent flurry of diplomatic activity, as the outside world seeks to support the reforms introduced by the new civilian-led government, our correspondent says.
On Tuesday, she met UN Secretary General Ban Ki-moon for the first time.
Mr Ban, who is on a three-day visit to Burma to encourage more democratic reforms, met Ms Suu Kyi at her house in Rangoon.
He said she had accepted an invitation to visit the United Nations headquarters in New York.
And Mr Ban said that he welcomed and respected her decision to compromise over the oath in the interests of the greater good.
"A real leader demonstrates flexibility for the greater cause of the people.
"I'm sure she'll play a very constructive and active role as a parliamentarian," he added.
The UN chief earlier called a further easing of sanctions on Burma as he addressed parliament.
He said he was encouraged by recent reform efforts in the country, but said the process of change was fragile and needed nurturing.
Ms Suu Kyi has said she supports retaining some restrictions to ensure that the pace of reform continues.
Mr Ban also held talks with President Thein Sein, a former military figure who has ushered in a series of reforms since he took office last year.