Single crystals of Ba2B5O9Cl with sizes up to 12 mm × 13 mm × 5 mm have been grown by top seeded solution growth method using LiF-H3BO3 as the flux for the first time. The TGA-DSC experiments proved that Ba2B5O9Cl melts incongruently. It crystallizes in the orthorhombic system, space group Pnn2, with unit-cell parameters a=1.1576(2) nm, b=1.1619(2) nm, c=0.66874(13) nm, V=0.8994(3) nm3, Z=4.There are BO3 and BO4 groups in the Ba2B5O9Cl crystal and it exhibits a three-dimensional network structure. Nonlinear optical efficiency of Ba2B5O9Cl is about 3.5 times that of KDP. The infrared spectrum and the UV-Vis diffuse reflectance spectroscopy were also performed on the reported material.