A release from the city police said they used online social media sites Saturday to move in and disrupt plans to stage a march and establish a second protest camp in a city park.
Mayor Sam Adams issued a statement saying "We simply cannot afford another encampment in our city," CNN reported.
Despite protesters' demands for First Amendment constitutional rights, the police statement said officers said they were justified in their evictions.
"Normal park hours are from 5 a.m. to 9 p.m., but due to the unsafe conditions and aggressive behavior by some demonstrators, the parks were ordered closed early," the release said, adding the protesters hadn't applied for any municipal permits to march and erect camps.
Portland Police Bureau spokesman Sgt. Pete Simpson told CNN both parks were cleared and quiet by 1 a.m.
The protest is part of the international movement that began earlier this year with Occupy Wall Street in New York that opposes corporate greed and income disparity between the rich and poor.