Jane Elizabeth Harley, Countess of Oxford and Countess Mortimer (née Scott; 1774–1824) was an English noblewoman, known as a patron of the Reform movement and a lover of Lord Byron.

She was a daughter of the Reverend James Scott, M.A., Vicar of Itchen Stoke in Hampshire and was brought up in favour of French Revolutionary thought and Reform.

In 1794 she married Edward Harley, 5th Earl of Oxford and Earl Mortimer (with her father taking the service), being styled Countess of Oxford and Countess Mortimer.

She frequently took lovers from among the pro-Reform party during her marriage, firstly Francis Burdett and most notably Lord Byron (the affair lasting from 1812, in the aftermath of Byron's affair with Lady Caroline Lamb, when he was fourteen years her junior, until 1813, when she and her husband went abroad but Byron did not follow as she had hoped).

Even in the easy-going world of the Regency aristocracy, her affairs were considered to have put her beyond the pale, and few people were prepared to receive her or call on her.