Nour was one of Rice's most honoured guests on Monday
Egyptian police have prevented opposition politician Ayman Nour from leaving the country to speak at the European Parliament, he says.
Mr Nour is due to stand trial next month for forging signatures on his party's registration documents.
The young lawyer called his treatment "unconstitutional". He says the charges against him are politically motivated.
On Monday, he was one of a number of opposition activists who met US Secretary of State Condoleezza Rice.
He was on his way to Strasbourg to address the parliament when he says he was stopped at Cairo's international airport.
"This is unconstitutional and it is politically motivated," Mr Nour told the Associated Press news agency.
Mr Nour will stand trial next week in a criminal court along with six other defendants from his al-Ghad (Tomorrow) party.
He says he hopes to stand against President Hosni Mubarak in country's first multi-candidate presidential elections due in September.
Mr Nour was released on bail on 12 March after six weeks in prison over the alleged forgery case. His detention without charge raised concern in Washington, which called for his release.
If he is convicted he would be disqualified from the presidential race.
On her recent visit Ms Rice criticised Cairo for cracking down on dissenters and called on it to ensure the upcoming election was free and fair. Among her talks with opposition figures on Monday, she held a 45-minute meeting with Mr Nour.