List of champions of the 1908 U.S. National Championships tennis tournament (now known as the US Open). The men's tournament was held from August 18 to August 29 on the outdoor grass courts at the Newport Casino in Newport, Rhode Island. The women's tournament was held from June 22 to June 27 on the outdoor grass courts at the Philadelphia Cricket Club in Philadelphia, Pennsylvania. It was the 28th U.S. National Championships and the second Grand Slam tournament of the three played that year.
See main article: 1908 U.S. National Championships – Men's singles. 
William Larned (USA) defeated Beals Wright (USA) 6–1, 6–2, 8–6
See main article: 1908 U.S. National Championships – Women's singles. Maud Barger-Wallach (USA) defeated Evelyn Sears (USA) 6–3, 1–6, 6–3
Fred Alexander (USA) / Harold Hackett (USA) defeated Raymond Little (USA) / Beals Wright (USA) 6–1, 7–5, 6–2
Evelyn Sears (USA) / Margaret Curtis (USA) defeated Carrie Neely (USA) / Miriam Steever (USA) 6–3, 5–7, 9–7
Edith Rotch (USA) / Nathaniel Niles (USA) defeated Louise Hammond Raymond (USA) / Raymond Little (USA) 6–4, 4–6, 6–4