| Official Name: | Mastamandau |
| Native Name: | माष्टामाडौं |
| Pushpin Map: | Nepal |
| Pushpin Label Position: | bottom |
| Pushpin Mapsize: | 300 |
| Pushpin Map Caption: | Location in Nepal |
| Subdivision Type: | Country |
| Subdivision Name: |  Nepal |
| Subdivision Type1: | Zone |
| Subdivision Name1: | Seti Zone |
| Subdivision Type2: | District |
| Subdivision Name2: | Achham District |
| Population As Of: | 2001 |
| Population Total: | 3411 |
| Population Density Km2: | auto |
| Population Blank1 Title: | Ethnicities |
| Population Blank2 Title: | Religions |
| Population Blank2: | Hindu |
| Timezone: | Nepal Time |
| Utc Offset: | +5:45 |
| Coordinates: | 29.25°N 81.24°W |
Mastamandau is a business center in Sanphebagar Municipality in Achham District in the Seti Zone of western Nepal. It was annexed to form the new municipality since 18 May 2014.[1] [2] At the time of the 1991 Nepal census, the village had a population of 2633 living in 547 houses.[3] At the time of the 2001 Nepal census, the population was 3411, of which 51% was literate.[3]