The crystal structures of the 3-aminophenol–H3PO4 (3-amphph) and 4-aminophenol–H3PO4 (4-amphph) complexes were determined at 100K. They both belong to the P212121 space group of the orthorhombic system with Z=4. The lattice parameters for the 3-amphph crystal are a=4.493(2)Å,b=9.750(3)Å and c=18.328(4)Å and those for the 4-amphph crystal are a=6.116(2)Å,b=7.496(2)Å and c=18.739(4)Å. The SHG powder efficiencies relative to KDP were 0.86 for 3-amphph and 0.50 for 4-amphph, measured at 1064nm using the Kurtz–Perry method. The infrared powder spectra of both complexes were obtained and the hydrogen bond vibrations are discussed.