Crystal structures of nitroguanidine chloride and nitroguanidine nitrate were solved by x-ray diffraction. The nitroguanidine chloride crystal is triclinic, space group P1, with unit cell parameters: a = 6·656(8)A, b = 6·719(9) A, c = 6·816(8)A, α = 66·8(2)°, β = 75·4(2)°, γ = 84·5(2)°, DC= 1·7g cm−3, Z = 2. The nitroguanidine nitrate crystal is monoclinic, space group P21/c with unit cell parameters: a = 4·587(4)A, b = 6·377(6)A, c = 21·167(15)A, β = 94·7(1)°, DC= 1·8g cm−3, Z = 4. EPR spectra were detected from crystals of both compounds which had been exposed to gamma or x-radiation. The EPR spectra are assigned to NO2and (NH2)2CN.