Single crystal of Pb2B5O9Cl with sizes up to 25 x 6 x 2 mm(3) has been obtained successfully using PbCl2-H3BO3 flux system by the high temperature solution method for the first time. It crystallizes in noncentrosymmetric orthorhombic space group Pnn2 (No. 34). It produces second harmonic generation (SHG) intensity about 4 times that of KH2PO4 (KDP) and is phase matchable. The origin and magnitude of the strong SHG effect was discussed. Band structures, density of states, and dipole moment calculations were calculated.