What was the name of Jane Austen's only sister?

Jane Austen’s only sister was Cassandra Austen. Cassandra Elizabeth Austen was Jane’s elder sister, born in 1773, two years before Jane.

The sisters were the only daughters among the eight children of George Austen and Cassandra Leigh. They were exceptionally close throughout their lives, sharing rooms, education, household responsibilities, and an extensive correspondence. Cassandra became Jane’s most trusted confidante, although many of her letters were later destroyed, probably to protect private family matters.

Cassandra also created the best-known contemporary image of Jane: a small pencil-and-watercolour portrait now associated with the National Portrait Gallery. Both sisters attended Reading Abbey Girls’ School briefly in 1785–1786, after earlier schooling in Oxford and Southampton. Neither married, and they remained closely connected as adults.

Names such as Anna and Mary can mislead quiz-takers because Anna was Jane’s niece and Mary was one of her sisters-in-law. Cassandra, however, was Jane Austen’s sole biological sister and lifelong companion.