A noncentrosymmetric nitrate, Pb-16(OH)(16)(NO3)(16), has been obtained using a hydrothermal method. It is constructed of [Pb-4(OH)(4)](4+) cubanes and nitrate form the overall three-dimensional structure via weak Pb-O bonds. Powder second-harmonic generation (SHG) using the Kurtz-Perry technique shows that Pb-16(OH)(16)(NO3)(16) is type I phase-matchable, and the measured SHG coefficient was 3.5 times that of KH2PO4. The direction and magnitude of the dipole moments in PbOn polyhedra and [NO3](-) triangles of Pb-16(OH)(16)(NO3)(16) have been quantified using the bond-valence approach, which shows that the large SHG response originates from the cooperation of PbOn polyhedra and [NO3](-) triangles. The band structure and density of states as well as electron density difference are calculated on the basis of density functional theory.