A new lead oxyborate, Pb4B6O13, has been successfully synthesized by introducing stereochemically active Pb2+ cations and distorted OPb4 tetrahedra into asymmetric borates. Pb4B6O13 exhibits an unprecedented two-dimensional (infinity)(B6O12)(6-) layer structure with a large second harmonic generation (SHG) response that is 3 times that of KH2PO4. In addition, theoretical work, including dipole moment calculations, electronic structure, and SHG coefficients combined with SHG density analysis, is reported. The results suggest that the enhanced SHG of Pb4B6O13 is attributed to the synergy effect of three functional units.