| Official Name: | Grajaú |
| Settlement Type: | Municipality |
| Pushpin Map: | Brazil |
| Pushpin Map Caption: | Location in Brazil |
| Coordinates: | -5.8189°N -46.1389°W |
| Subdivision Type: | Country |
| Subdivision Name: | Brazil |
| Subdivision Type1: | Region |
| Subdivision Name1: | Northeast |
| Subdivision Type2: | State |
| Subdivision Name2: | Maranhão |
| Subdivision Type3: | Mesoregion |
| Subdivision Type4: | Microregion |
| Subdivision Type5: | Metrop. region |
| Leader Title: | Mayor |
| Area Total Km2: | 8864 |
| Population Total: | 70,065 |
| Population As Of: | 2020 [1] |
| Population Density Km2: | auto |
| Timezone1: | BRT |
| Utc Offset1: | -03:00 |
| Postal Code Type: | Postal code |
| Area Code Type: | Area code |
Grajaú is a municipality in the Brazilian state of Maranhão. Founded on 29 April 1811, its population in 2020 was of 70,065. The total area is 8,864 km2.
It is one of the most important city in the south of the State. In Grajaú are located several industries of Plaster of Paris, as well as gypsum mining for other purposes (drywall, etc.). The city is the seat of the Roman Catholic Diocese of Grajaú.