"It is with great sadness that Mark and Carol Thatcher announced that their mother Baroness Thatcher died peacefully following a stroke this morning. A further statement will be made later," The Telegraph quoted her spokesperson Lord Bell, as saying.
Thatcher, who served from 1979 to 1990 as leader of the Conservative Party, was famously known as the 'Iron Lady' for her personal and political toughness.
Thatcher, who was a towering figure in post-war British and world politics, retired from public life after a stroke in 2002 and suffered several strokes after that.
Lady Thatcher will go down in history not only as Britain's first female prime minister, but also as the woman who transformed Britain's economy in addition to being a formidable rival on the international stage.
She was the only British Prime Minister to leave behind a set of ideas about the role of the state, which other leaders and nations strove to copy and apply.
Thatcher was born in Grantham, Lincolnshire, on October 13, 1925.