Chalcogenide borates were very rarely investigated in the past. As the second selenide borate, YSeBO2 obtained by a high-temperature solid-state reaction crystallizes in the noncentrosymmetric orthorhombic space group Cmc2(1) with a novel structure type. Its structure consists of two basic building units, [BO3](3-) planar triangles and [YO3Se4](11-) pentagonal bipyramids, and features the [YSeBO2]n planar belt. Second-harmonic-generation measurement shows its phase-matchable activity. YSeBO2 has an optical energy gap of 3.45 eV. Density functional theory calculation is also performed, addressing the electronic structure and nonlinear-optical property.