Mosier is a city in Wasco County, Oregon, United States. The population was 410 at the 2000 census.
Mosier was first settled in 1854 and incorporated as a city in 1914. The building now known as the post office was at that time the bank, and the original safe is still intact on-site. Mosier School was built in 1920 and until 1963 was a 1st–12th grade 1A school. From 1964 to 2002 it functioned as part of the Chenowith School District as an elementary school that ranged from Kindergarten to fifth grade. In January 2003, the Chenowith School District approved the charter application for Mosier Elementary to become a charter school known as Mosier Community School.
According to the United States Census Bureau, the city has a total area of 0.6 square miles (1.7 km²), of which, 0.5 square miles (1.2 km²) of it is land and 0.2 square miles (0.5 km²) of it (28.12%) is water.