The Personal Status Code (CSP), passed on August 13, 1956 by the country's first president Habib Bourguiba that helped shape the 1959 constitution, was considered a groundbreaking document in the Arab world.
The text made no reference to Sharia law, banned polygamy and mandated gender equality in the work place and in courts of law.
A collection of women's rights groups organised the rally Saturday to insist the rights enshrined in the CSP be incorporated into the new constitution to be drafted following October elections.
"We are celebrating the CSP this year," said Ahlem Belhaj, who heads the ATFD women's rights organisation.
But, she said, gender equality in Tunisia is "facing the threat of a loss in the gains" made in previous decades.
Tunisians will on October 23 elect representatives tasked with drafting a new constitution to govern the country following the ouster of former president Zine El Abidine Ben Ali, who fled Tunis on January 14 after a popular uprising.
The Ennahda Islamist movement, which was banned by the Ben Ali regime and only legalised in March, has considerable popular support and could become a strong political force, according to polls.
Ennahda representatives however, said women's rights groups have nothing to fear from their return to the political fold.
"Ennahda supports the gains of Tunisians, including the ban on polygamy which does not contradict the Koran," said Noureddine Bhiri, a party leader.
"Women were, along with men, victims of injustice under the Ben Ali regime, and it is time for them participate in governing," he added.
Some argued that Ben Ali, in power for 23 years, offered superficial support for women's rights to distance himself from Islamists, part of a strategy aimed at appeasing Western capitals who criticised his authoritarian tactics.