Katharine Waldo Douglas, CBE, (1870 – April 7, 1939) was an American novelist and translator.

She was born in New York City, the daughter of Henry Livingston Douglas and Hortense Pauline Armstrong.

Douglas wrote several books in the early 20th century, among them The Sign (1912), The Spare Room (1913), Shifting Sands (1914), The Rock (1915), The Basque Country (1921), and The Peacock's Tail (1925).

Douglas was actively involved in relief work in London during World War I and was decorated by King George V for her efforts.

Douglas died of injuries received in the crash of the Sud Express near Tolosa on March 29, 1939.