List of champions of the 1903 U.S. National Championships tennis tournament (now known as the US Open). The men's tournament was held from August 16 to August 24 on the outdoor grass courts at the Newport Casino in Newport, Rhode Island. The women's tournament was held from June 24 to June 27 on the outdoor grass courts at the Philadelphia Cricket Club in Philadelphia, Pennsylvania. It was the 23rd U.S. National Championships and the second Grand Slam tournament of the year. British Laurence Doherty became the first non-US winner of the men's championship.
See main article: 1903 U.S. National Championships – Men's singles. 
Laurence Doherty (GBR) defeated 
William Larned (USA) 6–0, 6–3, 10–8 [1]
See main article: 1903 U.S. National Championships – Women's singles. Elisabeth Moore (USA) defeated Marion Jones (USA) 7–5, 8–6 [2]
Reginald Doherty (GBR) / Laurence Doherty (GBR) defeated Kreigh Collins (USA) / Harry Wainder (USA) 7–5, 6–3, 6–3
Elisabeth Moore (USA) / Carrie Neely (USA) defeated Miriam Hall (USA) / Marion Jones (USA) 4–6, 6–1, 6–1
Helen Chapman (USA) / Harry Allen (USA) defeated Carrie Neely (USA) / W. H. Rowland (USA) 6–4, 7–5