List of champions of the 1888 U.S. National Championships (now known as the US Open). The men's tournament was held from August 22 to August 30 on the outdoor grass courts at the Newport Casino in Newport, Rhode Island. The women's tournament was held from June 12 to June 15 on the outdoor grass courts at the Philadelphia Cricket Club in Philadelphia, Pennsylvania. The men's doubles event was played at the Staten Island Cricket Club in Livingston, Staten Island, New York. It was the 8th U.S. National Championships and the second Grand Slam tournament of the year.:

Champions

Men's singles

🇺🇸 Henry Slocum defeated 🇺🇸 Howard Taylor 6–4, 6–1, 6–0

Women's singles

🇺🇸 Bertha Townsend defeated 🇺🇸 Ellen Hansell 6–3, 6–5

Men's doubles

🇺🇸 Oliver Campbell / 🇺🇸 Valentine Hall defeated 🇺🇸 Clarence Hobart / 🇺🇸 Edward MacMullen 6–4, 6–2, 6–2