Nubanusit Brook is a 14.3-mile-long (23.0 km) stream in southern New Hampshire in the United States. The brook begins at the outlet of Nubanusit Lake in Nelson. It is a tributary of the Contoocook River, part of the Merrimack River watershed. The brook flows south into Harrisville, interrupted by Harrisville Pond and Skatutakee Lake, then east to the MacDowell Reservoir (constructed for flood control) in Peterborough. The brook turns south, passes the village of West Peterborough, and reaches the Contoocook River after passing through Peterborough village.