The sub-Saharan migrants were trying to cross the Mediterranean to reach Italy.
It is the latest in a string of migrant boat capsizes off Tunisia's coast in the last few days, with five others sinking in the past four days.
This comes after Tunisia launched a campaign against undocumented African migrants.
Meanwhile, Italian officials on the island of Lampedusa say they are overwhelmed, after a record 2,500 migrants arrived in the last 24 hours.