Public assemblies of more than three people are officially banned under a state of emergency that has remained in place, along with a night-time curfew, since president Zine El Abidine Ben Ali was ousted last week.
The peaceful demonstrators were joined by hundreds of police officers, some of whom briefly blocked a car carrying interim president Foued Mebazaa, the speaker of parliament.
"The aim of this caravan is to make the government fall," said Rabia Slimane, 40, a teacher from Menzel Bouzaiane, where the first victim of the uprising was killed by security forces last month.
The General Union of Tunisian Workers, or UGTT, is refusing to recognise the new government because of its inclusion of figures from the old regime.
Ghannouchi has been prime minister in Tunisia since 1999. Following the revolt, he promised to resign from political life after Tunisia holds its first free and fair polls since independence from France in 1956.
US Secretary of State Hillary Clinton has called on Ghannouchi to carry out democratic reforms to stem the country's political turmoil.
Mebazaa has promised a "total break" with the old regime and the government has announced that political prisoners will be released and all political parties legalised.
Meanwhile the banned Islamist movement Ennahdha has said it intends to register as an official political party and take part in elections.
The government on Saturday also lifted restrictions on the import of foreign literature and films, which were tightly controlled by the previous regime.
Schools and universities, which were shut on January 10 in the final days of Ben Ali, are to be reopened this week.