The London mayor has dual nationality as he was born in New York - but has now revealed he wants to hand back his American passport.
"The reason I'm thinking I probably will want to make a change is that my commitment is, and always has been, to Britain," he told the Sunday Times during a week-long tour in the States.
"It's an accident of birth that has left me with this thing. I've got to find a way of sorting it out."
Johnson - who is running for parliament in Uxbridge and South Ruislip - said he would approach US ambassador Matthew Barzun about the change. "It is a laborious business. They don't make it easy for you," he added.
Constitutional experts believe dual nationality would not present any technical barrier to Johnson becoming prime minister, but he would be likely to face questions about his loyalties.
Aides said the mayor's priority was to avoid paying more to the US tax authorities, after he was recently forced to settle a large capital gains tax bill.