Nashua High School South, formerly known as Nashua Senior High School, is a public high school located in Nashua, New Hampshire. The school's current location was erected in 1975 with its first class graduating in June 1976. The school was remodeled between 2002 and 2004 when a second school, Nashua High School North, was built. The existing high school building was renamed Nashua High School South. The school serves approximately 1800 students, making it the largest public high school in New Hampshire, and the second largest high school overall, after the private Pinkerton Academy.

Nashua is a city in southern New Hampshire, United States. As of the 2020 census, it had a population of 91,322, the second-largest in northern New England after nearby Manchester. Along with Manchester, it is a seat of New Hampshire's most populous county, Hillsborough.