Mirna may refer to:
- geographical entities
- Mirna (Croatia), a river in Istria, Croatia
- Mirna (Sava), a river in Slovenia, right tributary of the Sava River
- Mirna (settlement), a settlement in the Municipality of Mirna in southeastern Slovenia
- Mount Mirna, a hill in the Municipality of Semič, southeastern Slovenia
- people
- Mirna (name)
- Mirna Jukić, a bronze medal winner in swimming
- Mirna Khayat, a Lebanese music video director
- other
- microRNA, abbreviated as miRNA
- USS Mirna (SP-1214), a United States Navy patrol boat in commission from 1917 to 1918