On a sentimental final trip to Germany as president, Obama expressed hope that the New York businessman who has never previously held public office would jettison controversial campaign rhetoric when he entered the White House and keep democratic values in mind as he chose his staff.
Republican Trump defeated former Secretary of State Hillary Clinton, a Democrat, in an upset election after criticizing his opponents in sharply-worded blasts on Twitter, promising to build a wall on the US border with Mexico, and pledging to ban Muslims temporarily from entering the United States.
He also praised Russian President Vladimir Putin, whose annexation of Crimea from Ukraine led to western sanctions.
Obama, who along with Merkel called for those sanctions to be renewed until Russia complied with international agreements, said he hoped Trump would be pragmatic in dealing with Washington's former Cold War foe.
"My hope is that he does not simply take a realpolitik approach and suggest that we just cut some deals with Russia even if it hurts people, even if it violates international norms or even if it leaves smaller countries vulnerable or creates long term problems in countries like Syria," Obama said.
Obama said he had spoken to Putin before the US election about cyber attacks that US officials said were an attempt to influence the presidential race and told him Washington would respond appropriately. Moscow has dismissed the allegation.