Pennichuck Brook is one of the tributaries of the Merrimack River in New Hampshire in the United States.

Its watershed is 31 square miles (80 km2) and is one of the 14 subwatersheds of the Merrimack River.

[1] Pennichuck Brook begins at Silver Lake in Hollis.

It flows northeast under NH 122 and into Dunklee Pond, then continues northeast into Pennichuck Pond, on the boundary between Hollis and Nashua.

While part of Bowers Pond, it is crossed by the Everett Turnpike.