Tomorrow she will meet with Trump in the Oval Office and focus on priorities such as a post-Brexit trade deal and co-operation on security issues like Syria, counter-terrorism and Russia.
May is expected to stress the value of international institutions like Nato, after Trump declared the military alliance "obsolete" on the campaign trail.
Downing Street also hopes it will allow May to get to know Trump and establish a "strong and productive working relationship" with the new president.
May told reporters on the flight to the United States that she and Donald Trump will form a close bond because "opposites attract".
She rejected any claims that there could be a "potential character clash" between her and Trump and made clear she is looking forward to speaking to him "face-to-face" about the issues facing Britain and America.
It follows a backlash from MPs who have accused her of "cosying" up to Trump despite his controversial comments.
In Washington. a raft of foreign service officials resigned from the US State Department indicating they did not want to serve in a Trump administration.
