Bella Sidney Woolf OBE (1877–1960) was an English author. Her writings predominately draw on her experience living overseas in British colonies. Through her brother Leonard Woolf, she is the sister-in-law of author Virginia Woolf.

Woolf was born in London, the eldest (or 2nd eldest) of ten children to Marie (née de Jongh) and the Jewish barrister Solomon Rees Sydney Woolf. Her father died in 1892.

At the end of 1907, she travelled to Ceylon (today known as Sri Lanka) to visit her brother, Leonard Woolf, then a junior civil servant stationed in Kandy.

In the following months she met Robert Heath Lock, Assistant Director of the Peradeniya Botanical Gardens. They were married in 1910. In August 1908, she returned to England with her brother, who was returning briefly before taking up a promotion as Assistant Government Agent of Hambantota. Lock died in 1915.

In 1921, Woolf married Tom Southorn, whom she met in Ceylon. Following his service in Ceylon, Southorn served as the colonial secretary of British Hong Kong, Acting Administrator of Hong Kong, and Governor of Gambia.

After her marriage, Woolf sometimes went by Bella Woolf Southorn, and occasionally Bella Sidney Southorn, but continued to publish as Bella Sidney Woolf.

From 1926 to 1936, Woolf acted as commissioner of the Girl Guides in Hong Kong. In 1935 she was appointed an OBE.

Woolf wrote fiction and non-fiction. In both she drew on her experiences in British colonies. She also authored and co-authored writings on current events and science.