List of champions of the 1900 U.S. National Championships tennis tournament (now known as the US Open). The men's tournament was held from August 13 to August 21 on the outdoor grass courts at the Newport Casino in Newport, Rhode Island. The women's tournament was held from June 19 to June 23 on the outdoor grass courts at the Philadelphia Cricket Club in Philadelphia, Pennsylvania. It was the 20th U.S. National Championships and the second Grand Slam tournament of the year.
See main article: 1900 U.S. National Championships – Men's singles. 
Malcolm Whitman defeated William Larned 6–4, 1–6, 6–2, 6–2
See main article: 1900 U.S. National Championships – Women's singles. Myrtle McAteer defeated Edith Parker 6–2, 6–2, 6–0
Holcombe Ward / Dwight Davis defeated Fred Alexander / Raymond Little 6–4, 9–7, 12–10
Hallie Champlin / Edith Parker defeated Marie Wimer / Myrtle McAteer 9–7, 6–2, 6–2
Margaret Hunnewell / Alfred Codman defeated T. Shaw / George Atkinson 11–9, 6–3, 6–1