This was the second demonstration this year against the death sentence, which is carried out in Lebanon by hanging for civilians and by firing squad for soldiers.
Ten convicted murderers are scheduled to be executed in the country in the coming months.
Most of the demonstrators were dressed in black as a sign of their "mourning for justice twice killed - first by a crime and then by an execution," said a representative of the Movement of People's Rights which organised the demonstration.
In front of the government offices and surrounded by police, children uncovered the "hangmen," dismantled the gallows and used the ropes to play skipping games.
In January, the movement's spokesman, Walid Slaibi, said the Lebanese leadership intended to carry out death sentences that had been blocked by former prime minister Salim Hoss.
Hoss unwilling
During his term in office Mr Hoss refused to sign the decree of execution of two people, citing his "own convictions", in March 2000.
"I cannot act against my convictions. I cannot imagine signing any death sentence whatsoever. God gives life and only he can take it away," he said.
A total of 17 people have been executed in Lebanon since 1994 when the current law stripping judges of their right to show leniency came into force.
The law and the executions which followed it have been strongly condemned by human rights organisations.
All the executions were carried out under the former president of the republic Elias Hrawi, with a counter signature of Prime Minister Rafiq Hariri, who returned to the post last year.