The singer was entering her house in Blackburn, West Lothian, late Tuesday when the unexpected guest ran out past her.
A police statement said Wednesday, "Lothian and Borders Police were called to an address in Blackburn at around 9:50 p.m. yesterday following reports of a disturbance. A man was detained in connection with the incident and released without charge pending further inquiries."
Boyle's rep also said Wednesday: "Last night, Susan returned home with a friend and found an intruder in her house. She was shocked but unharmed."
Despite her current best-selling album and recent rise to riches, Boyle, 48, remains living in the same humble, local authority housing residence she grew up in.
At the time she encountered the intruder, Boyle had just returned from London, where she was recording her part for Simon Cowell's charity version of REM's Everybody Hurts, to raise money for Haiti relief.