Hundreds of demonstrators, along with relatives of those killed by the HIV-infected blood, held up pictures of the dead children, as well as mock coffins and black flags as Parvanov arrived at Tripoli's airport on Friday.
The Bulgarian president was officially greeted by Libyan Foreign Minister Abdelrahman Shalgham and General Mustafa Karrubi, a member of the revolutionary command.
Parvanov's two-day visit, on the invitation of Libyan leader Muammar al-Qadhafi, comes days before the supreme court in Tripoli is expected to rule on the appeal of the medical workers.
Last year, the medical workers - five Bulgarian nurses and a Palestinian doctor - were sentenced to death on charges of intentionally infecting the children with HIV-contaminated blood as part of an experiment to find a cure for Aids.
Parvanov was cautious about the outcome of his trip, warning against high expectations.
"The purpose of the visit is to reinstate the dialogue" with Libya, he said in a TV interview ahead of the visit, which is the first by a Bulgarian leader to Libya since the end of the communist era.
Parvanov was expected to meet the nurses, who are being held in Tripoli's Judeyda prison. No further details about the trip were immediately known.
Parvanov (R) is expected to
meet the nurses in jail
On Tuesday, EU External Relations Commissioner Benita Ferrero-Waldner visited al-Qadhafi in Tripoli to appeal for the release of the medical workers. Ferrero-Waldner said she did not talk about compensation with al-Qadhafi but urged him to work for the prisoners' release. She said "the response of al-Qadhafi clearly was he could not interfere with the judiciary".
She said the EU still had "confidence in the independent judiciary of Libya" but added she "clearly expressed reservations on evidence on which they have been convicted".
Human rights groups have accused the Libyan government of concocting the charges to cover up unsafe practices in the country's hospitals and clinics. The United States, Europe and Bulgaria have pressed Libya to free the medical workers, who were convicted in May 2004.
Libya has called on Bulgaria to pay compensation to the victims' families, but Bulgaria has rejected that demand.
Libyan officials have suggested that the death sentence could be reconsidered if the families of the victims were compensated and those still alive were treated.