Hydroxylammonium nitrate (HAN) is the main active toxic component of the new HAN-based liquid propellant. It is a moderately toxic and caustic substance to animals, and can be administrated through dermal, oral or respiratory route. HAN causes severe damage to skins, eyes, and red blood cells of the hematologic system. Significant signs of HAN poisoning include hemolytic anemia, methemoglobinemia, splenomegaly, erythrocyte destruction and Heinz body formation. This review summarize the toxicity of hydroxylammonium nitrate, and discuss the primary protection methods.