Speaking at the G20 summit in Hamburg, he said he would go to London. Asked when, he said: "We'll work that out".
The US president was speaking ahead of talks with UK Prime Minister Theresa May to discuss post-Brexit trade deals.
It was one of a series of one-to-one meetings with world leaders which will also see Mrs May hold trade talks with Japanese Prime Minister Shinzo Abe.
Before their meeting, Mr Trump hailed the "very special relationship" he had developed with Mrs May.
"There is no country that could possibly be closer than our countries," he told reporters.
"We have been working on a trade deal which will be a very, very big deal, a very powerful deal, great for both countries and I think we will have that done very, very quickly."
resources : bbc