Rebecca Sieff

Rebecca Dora Sieff (; ; 23 February 1890 – 8 January 1966) was a British Zionist and feminist. Sieff was a founding member and director of the Women's International Zionist Organization. Her father was born to a Polish–Jewish family in Slonim, Grodno Governorate (present-day Belarus) and her mother was from a Russian-Jewish family. The second of five siblings, Sieff was the younger sister of the Simon Marks (later Baron Marks).

She was involved in the formation of the Women's International Zionist Organization (WIZO), In 1919 she and Vera Weizmann, Olga Alman, and Romana Goodman persuaded the English Zionist Federation that a separate organisation for women was required. Sieff was the first President of the new organisation.

In 1934, the Sieff family endowed the establishment of the Daniel Sieff Research Institute in memory of their Daniel (1915–1932), who intended to be a scientist. The institute was renamed the Weizmann Institute of Science in 1949 with the Sieff family's consent.

On 8 January 1966, Sieff died at the Tel Aviv Sourasky Medical Center aged 75.