The Mier expedition is an unsuccessful military operation launched in November 1842 by a Texian militia against Mexican border settlements; it is related to the Somervell expedition.

It includesa major battle at Ciudad Mier on December 26 and 27, 1842, which the Mexicans win.

The Texian attack is launched partly in hopes of financial gain and partly in retaliation for the Dawson Massacre (as named by Texans) earlier that year, in which thirty-six Texas militia had been killed by the Mexican Army

Both conflicts are part of continuing efforts by each side to control the land between the Rio Grande and Nueces River.

The Republic of Texas believes that this territory had been ceded to it in the Treaties of Velasco, by which they gained independence; but Mexico does not agree.