The ferry sank in Shandhya river in Banaripara upazila of Barisal district, police said.
The body of an unidentified woman has been recovered by rescuers while an operation to locate other missing people was underway, said SM Akhteruzzaman, superintendant of police.
ML Oishi with around 60 people on board, capsized at Dasherhaat point while its passengers started to get down after it anchored there, the Dailystar online reported citing the police.
Some people are believed to have swam ashore.
In February last year, 69 people died in central Bangladesh in a boat mishap.