The incident happened on Thursday (November 7) at around 5pm where the man entered the 81-year-old woman's home demanding money.
He was armed with a hammer.
A Lancashire Police spokesman said she was left extremely frightened and upset. She was not physically hurt.
Enquiries are now on-going to identify the offender who is described as 5ft 9ins tall and slim build.
He spoke with a foreign accent and was wearing a black jacket with a high visibility vest over the top.
Detective Constable Sarah Whittaker, of Burnley CID, said: “This must have been an absolutely terrifying experience for this elderly lady.
"It is fortunate that she was not physically hurt during this unnerving ordeal.
"We have a number of enquiries ongoing and I would appeal for the public’s help so we can identify this offender."
Anyone with information should call police on 101 quoting log 1273 of November 7 or independent charity Crimestoppers on 0800 555 111.