| Castellar del Riu | |
| Settlement Type: | Municipality |
| Mapsize: | 200px |
| Pushpin Map: | Spain Province of Barcelona#Spain |
| Pushpin Label Position: | left |
| Pushpin Map Caption: | Location in Catalonia |
| Coordinates: | 42.1331°N 1.71°W |
| Subdivision Type: | Country |
| Subdivision Name: |  Spain |
| Subdivision Type1: | Community |
| Subdivision Type2: | Province |
| Subdivision Name2: | Barcelona |
| Subdivision Type3: | Comarca |
| Subdivision Name3: | Berguedà |
| Leader Party: | CiU |
| Leader Title: | Mayor |
| Leader Name: | Adrià Solé Giralt (2015)[1] |
| Area Footnotes: | [2] |
| Area Total Km2: | 32.7 |
| Elevation M: | 1234 |
| Population Density Km2: | auto |
| Population Demonym: | Castellanenc |
Castellar del Riu (pronounced as /ca/) is a municipality in the comarca of Berguedà, Catalonia, northern Spain. The municipal government is located at Llinars, which is not a village but just a few municipal buildings including a small sports centre.
The municipality's economy is principally centered on agriculture, and in particular dryland farming and animal husbandry. There is also small-scale tourism in the municipality, to the Pi de les Tres Branques (a monumental tree which is a popular venue for Catalan nationalist gatherings), and especially the ski station of Rasos de Peguera.