Police officers threw teargas canisters at worshippers inside the Saint-Pierre Catholic Church in Pétion-Ville on Thursday.
Many were injured and several fainted. They were transported to the hospital.
The mass was being held to protest against the ongoing violence. Protesters also set vehicles on fire near the church and marched inside with signs.
Some Catholic churches in the United States, Canada, France were held mass to call for an end to the ongoing violence in Haiti at the same time.