Dozens of demonstrators, some shouting "Down with the UN," threw stones, broke UN vehicles' windshields, and burned a US flag.
No arrests were made. Some damage was reported but there were no immediate reports of injuries, authorities said.
The protest took place as UN and Haitian government officials attended a ceremony here marking the 61st anniversary of the creation of the world body.
The United Nations has been in Haiti since June 2004 with more than 7,000 troops and 1,200 police sent to help stabilise the poorest country in the Americas.

Copyright AFP (Agence France-Presse), 2006