Sirna may refer to:

• Sírna, legendary High King of Ireland

• Șirna, a commune in Prahova County, Romania

• Sirna, Iran, a village in Markazi Province, Iran

• Small interfering RNA (siRNA)

• Syrna, also spelled Sirna, Greek village

• Syrna (island), also spelled Sirna, Greek island

• Sirna Therapeutics