American physician and educator who struggled for the rights of women to learn, practice, and teach medicine in the mid-1800s.

Preston was educated in Quaker schools and later became active in the abolition (abolitionism) and temperance (temperance movement) movements. Her temperance work had aroused in her an interest in physiology and hygiene, and she studied those subjects as well as Latin on her own for a time. She began to teach classes in physiology and hygiene to other interested women and in 1847 became a medical apprentice in the office of a physician friend in Philadelphia. Two years later, having completed her apprenticeship, Preston was refused admission to all four Philadelphia medical colleges because of her sex. In October 1850, however, she entered the newly established Female (later Woman's) Medical College of Pennsylvania with the first class, and she graduated in 1851. After further study she was appointed professor of physiology and hygiene at the college in 1853.

In 1858 the Board of Censors of the Philadelphia Medical Society effectively banned women physicians from the public teaching clinics of the city. In order to provide vital clinical experience to the college's students, Preston began raising funds for a women's hospital to be affiliated with the college. A board of women managers, of which she was a member, was appointed to direct the planning and operation of the hospital. The college closed on the outbreak of the Civil War in 1861, but the Woman's Hospital opened later that year. The Woman's Medical College, operating under a new charter, opened the following year. In 1863 Preston worked with Emeline H. Cleveland (Cleveland, Emeline Horton), chief resident of Woman's Hospital, to establish a training school for nurses, and in 1866 Preston was chosen first woman dean of the college. She continued in that post as well as in her professorship for the rest of her life.

Under Preston's leadership the students of the Woman's Medical College were at last admitted to the leading general clinics in Philadelphia in 1868. The following year, in response to a remonstrance by other local medical colleges and hospitals and numerous individual doctors, she published in the Philadelphia newspapers a classic argument in support of women physicians.