The organizers of the protest in northern Germany, which came four days before the start of the G8 summit in nearby Heiligendamm, have claimed that at least 165 people were arrested.
Police said 433 officers were injured in the clashes, 30 seriously.
Police said the violence involved only a small percentage of the 20,000 people that took part in the march.
"It was about Africa, climate change and poverty, but there was another face to the demonstration, where we had to bow to violent protesters which we couldn't change," Greenpeace spokesman Carsten Smid told Reuters. "Our de-escalation tactic failed. "
(AFP, AP, Reuters)