The 48-year-old church volunteer was speaking in the first part of a two-stage interview on the show in the US on Monday.
Ms Boyle was the star guest as Winfrey was joined by TV judge Simon Cowell for a show called The World's Got Talent.
The first part was pre-recorded at her home in Blackburn, Scotland. The subtitles were added by bosses who thought American viewers would not understand her strong Scottish accent.
They were dropped during Ms Boyle's live interview with Winfrey.
The singer later told Winfrey that the global fame she had achieved was "like a dream come true".
Ms Boyle has been watched by millions of internet viewers since she first stunned judges with her rendition of I Dreamed A Dream from the musical Les Misèrables.
It has turned her into a global phenomenon with celebrity fans including the actress Demi Moore.
She has already appeared on several US TV programmes including Larry King Live, the veteran interviewer's CNN show.
Boyle remains favourite to win Britain's Got Talent but faces competition from fellow singer Jamie Pugh, the Welsh pizza delivery man who overcame stage fright to sing a tune from Les Misèrables.
However, his chances were dealt a blow when it was disclosed that he had sung in a West End theatre before, contradicting his claim that he had never performed before a large crowd.