The 1931 U.S. National Championships (now known as the US Open) was a tennis tournament that took place on the outdoor grass courts at the West Side Tennis Club, Forest Hills in New York City, United States.

The tournament ran from September 3 until September 10.

It was the 51st staging of the U.S. National Championships and the fourth Grand Slam tennis event of the year.

[1] Ellsworth Vines defeated George Lott 7–9, 6–3, 9–7, 7–5 Helen Wills Moody defeated Eileen Bennett Whittingstall 6–4, 6–1 Wilmer Allison / John Van Ryn defeated Gregory Mangin / Berkeley Bell 6–4, 8–6, 6–3 [2] Betty Nuthall / Eileen Bennett Whittingstall defeated Helen Jacobs / Dorothy Round 6–2, 6–4 [3] Betty Nuthall / George Lott defeated Anna McCune Harper / Wilmer Allison 6–3, 6–3 [4]