The electronic structure, dielectric, piezoelectric, and nonlinear optical properties of recently synthesized polar iodate BiO(IO3) are systematically investigated by density functional theory calculations. The energy band structure shows that it is an indirect-band-gap semiconductor. The analyses of its zone-center phonon modes, it is found that there are 17A1, 18A2, 17B1, and 17 B2 optical phonon modes. The elastic stiffness tensors satisfy the Born stability restriction, indicating that this compound is mechanically stable. Importantly, the large piezoelectric and nonlinear optical susceptibilities show that polar iodate BiO(IO3) is a highly competitive piezoelectric and nonlinear optical material.