During the demonstration in the capital Bamako, which organisers say attracted 10,000 people, protesters held signs reading "Don't touch my Constitution", "No, means no" and "No to the referendum".
The protest, which authorities said was not authorised under the state of emergency, took place on the eve of the so-called "G5 Sahel" summit aimed at consolidating Western backing for a regional anti-jihadist force.
French President Emmanuel Macron is due to fly in Sunday for the summit, joining leaders from the "G5 Sahel" countries just south of the Sahara -- Burkina Faso, Chad, Mali, Mauritania and Niger.
"A large part of Mali is occupied," local activist Moussa Keita told AFP, referring to jihadists in the north and centre of the country.
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"It is more urgent to liberate the country than to organise a referendum," he said.
The referendum, which was due to be held on July 9 but has since been delayed because of fierce opposition, would enshrine elements of a 2015 peace deal in the charter and establish a senate in parliament.
Tuareg-led rebels led an uprising in 2012 that was hijacked by jihadists, throwing Mali into chaos and triggering a UN-French military intervention the following year.
The referendum is opposed by those who say it gives President Ibrahim Boubacar Keita excessive powers and claim that a vote cannot be held safely in the troubled north, which remains wracked by jihadist violence and a near absence of state authority.
"We came once again to call for the withdrawal of the referendum," former minister Sy Kadiatou Sow, known as the "Iron Lady" of Malian politics, told AFP.
Sow is part of the "Don't touch my constitution" group, which wants to see the referendum retracted and a national consultation held to rewrite it.
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