Vuk Draskovic, the Serbian foreign minister, and his Montenegrin counterpart Miodrag Vlahovic signed a protocol on Thursday in Belgrade establing diplomatic ties between the two.
"Political parties, decisions... everything is temporary, but special relations between Serbia and Montenegro are not," said Draskovic after the signing of the protocol.
Vlahovic said the two republics "are together again in the capacity which enables them to be equal."
"Montenegro has not fulfilled its independence to build a fence around itself or to rise up barriers, but on the contrary, to cooperate," he said.
In a May referendum, 55.5% of voters opted to break away from Serbia. On June 3, after more than eight decades of union, Montenegro's parliament proclaimed independence, although Serbia only officially recognised it 12 days later.
Belgrade had openly supported those in Montenegro who had opposed separation, with Prime Minister Vojislav Kostunica hardly hiding his dissatisfaction with the outcome of the vote.
Serbia and Montenegro had been united in various forms since 1918. Their last joint state was a loose union that had replaced Yugoslavia in 2003.