Two days before his state visit to the UK, Mr Trump waded into the leadership race seeing 12 MPs battle it out to get into Downing Street.
He said to The Sun: "I actually have studied it very hard. I know the different players. But I think Boris would do a very good job. I think he would be excellent. I like him. I have always liked him.
"I don't know that he is going to be chosen but I think he is a very good guy, a very talented person."
Last week the US leader said he could meet Nigel Farage and Mr Johnson during his state visit to the UK next week.
The US President claimed other candidates had approached him in a bid to secure his endorsement: “Other people have asked me for an endorsement, too. I have been asked for endorsements.
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“I could help anybody if I endorse them. I mean, we’ve had endorsement where they have gone up for 40, 50 points at a shot.”
The US leader also said he liked Tory party leader contender Jeremy Hunt but not Michael Gove due to his stance on Iran.
Mr Trump and his wife Melania will arrive in the UK on Monday, June 3 and will stay until Wednesday, June 5.
The Trumps will be honoured with a ceremonial welcome in the gardens of Buckingham Palace on the first day of the three-day trip, featuring royal gun salutes and a guard of honour.
When Mr Trump visited the UK last year, he sparked an upset by telling Mrs May that Mr Johnson would make a good prime minister.