Mojmir I, Moimir I or Moymir I is the first known ruler of the Moravian Slavs (820s/830s–846) and eponym of the House of Mojmír.

In modern scholarship, the creation of the early medieval state known as "Great" Moravia is attributed either to his or to his successors' expansionist policy.

He is deposed in 846 by Louis the German, king of East Francia.