Ibrahim was convicted on similar charges in the early 2000s
Human rights activists in Egypt have criticised as undemocratic a two-year prison sentence handed down to a prominent civil rights campaigner.
Saad Eddin Ibrahim, who lives in exile, was convicted on charges of tarnishing Egypt's reputation.
Activists say it is the verdict that harms the country's image rather than Mr Ibrahim's campaign.
The charges were brought after he urged President George W Bush to link further US aid to Egypt to democratic reforms.
Mr Ibrahim, who also has American citizenship, has said he will appeal against the verdict.
Human rights activists say the legal system is being used to silence opposition to President Hosni Mubarak.
The BBC's Magdi Abdelhadi says charges of tarnishing Egypt's reputation are often brought against critics of Mr Mubarak by people with links to his governing party, rather than by the public prosecutor.
Mr Ibrahim went into exile several months ago fearing arrest if he returned to Egypt after he published a series of articles critical of Mr Mubarak's government.
He was sentenced to seven years in jail in 2002, also for defaming Egypt, but was released on appeal after spending nearly a year behind bars.