| Frazier Brook | |
| Pushpin Map: | New Hampshire#USA |
| Pushpin Map Size: | 250 px |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | New Hampshire |
| Subdivision Type3: | County |
| Subdivision Name3: | Merrimack |
| Subdivision Type4: | Towns |
| Subdivision Name4: | Danbury, Wilmot, Andover |
| Length: | 7.7miles |
| Source1 Location: | Danbury |
| Source1 Coordinates: | 43.5208°N -71.8747°W |
| Source1 Elevation: | 940feet |
| Mouth: | Blackwater River |
| Mouth Location: | Andover (Cilleyville) |
| Mouth Coordinates: | 43.4311°N -71.8683°W |
| Mouth Elevation: | 644feet |
Frazier Brook is a 7.7adj=midNaNadj=mid[1] stream in central New Hampshire in the United States. Via the Blackwater and Contoocook rivers, it is part of the Merrimack River watershed. It is subject to the New Hampshire Comprehensive Shoreland Protection Act.
Frazier Brook begins in Danbury, New Hampshire, just south of the town center, and flows south through the town of Wilmot into Andover. Eagle Pond and Bog Pond interrupt the brook's flow. Shortly below Bog Pond, the brook reaches the Blackwater River at the village of Cilleyville.
Frazier Brook is paralleled for most of its length by U.S. Route 4.