Thousands of protesters are converging on the venue of an EU summit where George W Bush is due to meet 15 European Union leaders.
Police are expecting about 12,000 people to join rallies in Gothenburg scheduled for throughout the day.
Mr Bush arrived in Sweden from Brussels, Belgium, for the latest stop of his European visit.
His talks with the European leaders are expected to be dominated by his plans for a missile defence shield.
More than 80 protest groups are expected to take part in rallies, which leaders insist will be peaceful.
But several shop owners have boarded up their stores in anticipation of violence.
Some groups are opposing specific US policies, such as the death penalty and Mr Bush's rejection of the Kyoto agreement to limit greenhouse gas emissions.
Many protesters are concerned that global corporations have gained too much control and exploit the poor and the environment. Much of their anger is directed at the US, home of many of the world's largest multinational corporations.
Protesters have been preparing for days and about 3,000 of them have been sleeping in makeshift accommodation.
Swedish Prime Minister Goeran Persson, who met about 400 representatives of the protest groups yesterday, has asked them to avoid violence.