Serbia has formally declared its independence in response to Montenegro's vote to secede.
Sadness at the break-up contrasted with the mood in Montenegro
At a special televised meeting, parliament declared Serbia the legal successor to the defunct union of Serbia and Montenegro.
It also gave all state institutions 45 days to complete the separation.
The BBC's Nick Hawton in Belgrade says the solemn meeting contrasted sharply with the street celebrations which marked Montenegro's independence.
Under the constitutional charter of the union, Serbia now inherits membership of the United Nations and other international institutions, leaving Montenegro to apply in its own right.
The union of Serbia and Montenegro was the last vestige of what was once the six-member Yugoslav federation.
Montenegro narrowly voted in favour of independence in a referendum last month.
One of Serbia's first tasks will be to change flags on government buildings.
"I conclude the vote and hereby announce that 126 MPs voted in favour, with none against," said Serbian parliament speaker Predrag Markovic.
After a series of devastating wars, dictatorship and economic sanctions, Serbia stands alone - more streamlined, more simplified, but still with major issues ahead, including the future of the province of Kosovo, our correspondent reports.