A crowd cheered Nur as he left a Cairo detention centre after supporters paid his bail of 10,000 Egyptian pounds ($1735), party officials said on Saturday.
Nur, who is leader of the opposition Al-Ghad (Tomorrow) party, had been held for about six weeks during investigations into allegations that his party forged documents when it applied for recognition last year.
The al-Ghad party has dismissed the allegations as politically motivated fabrications.
Public prosecutor Mahir Abd al-Wahad had earlier ordered Nur and five others to be freed on payment of bail of 10,000 pounds each, but said the investigation was continuing.
The United States has said it has "very strong concerns" about the Nur case.
Nur is permitted to continuing his
But Nur, who has said he intends to run for president under plans to allow multi-candidate elections in Egypt, has said he does not want any foreign intervention on his behalf.
"Ayman is released now and he is in the middle of quite a large crowd," Wail Nawara, an aide to Nur, told Reuters by telephone from the scene, speaking over the clamour of a cheering crowd.
He said Nur was being taken on top of a pick-up truck to a
celebration to mark his release.
Party officials said Nur had personally refused to pay bail to secure his own release, but supporters collected the funds to pay it anyway.
Nur had been transferred on Saturday from a prison to the Cairo detention centre from where he was released, they said.
"Ayman is released now and he is in the middle of quite a large crowd"
Aide Wail Nawara
A judicial source said Nur, who is a member of parliament, could continue his political activities, provided there was no final court ruling against him.
"His parliamentary immunity was lifted for the investigation, but it does not affect his membership of parliament," the source said.
A close associate of Nur, Ayman Barakat, left jail on Friday after more than five weeks of detention for questioning in connection with the allegations against Nur.
Nur has been a vocal advocate of constitutional change and welcomed President Husni Mubarak's proposal last month to change the constitution to allow multi-candidate elections to replace the existing single-candidate referendum.
He announced his intention to run for the presidency in the first edition of the party's newspaper that came out this week.
The proposal to amend the constitution is working its way through parliament.
Other opposition parties have also welcomed Mubarak's proposals, but some have also voiced concerns that parliament, which is dominated by Mubarak's ruling National Democratic Party, will put so many conditions on who can run that it will render any presidential race meaningless.