A new deep-ultraviolet nonlinear optical phosphate, LiRb2PO4, has been grown by the top seeded solution growth method. Its structure was determined by single-crystal X-ray diffraction. It crystallizes in the orthorhombic space group Cmc2(1) and reveals a three dimensional framework composed of isolated PO4, LiO4 tetrahedra and RbOn polyhedra (n = 8 and 10). The powder second-harmonic generation efficiency (SHG) measurements reveal that LiRb2PO4 displays a remarkable SHG effect 2.1 times that of KDP. Moreover, LiRb2PO4 is type-I phase-matchable. Remarkably, LiRb2PO4 was observed to possess a large transmission region with the cut-off edge below 170 nm. These excellent properties make LiRb2PO4 a possible deep-ultraviolet nonlinear optical crystal. An analysis of theoretical calculations by density functional theory was made to illustrate the relationships between the structure and the properties of LiRb2PO4.