Metal oxyhalides have attracted broad interest recently because of their diverse structures and versatile properties. Here, two oxyhalides, CuSb 2 O 3 Cl (1) and CuSb 2 O 3 Br (2), were studied by focusing on their nonlinear-optical properties. They are crystallized in the noncentrosymmetric monoclinic Cc structure, and the layered structures could be derived from a 1:1 combination of CuX-(X = Cl, Br) and Sb 2 O 3 -type slabs. Their energy gaps were determined to be 2.76 and 2.64 eV. The second-harmonicgeneration (SHG) test suggests that they are nonlinear-optical-active, and the effects are ascribed to the contribution of CuX 3 O units. Meanwhile, the SbO 3 units' arrangement has a small contribution to the SHG effects. This work is the pioneer SHG investigation of the M I −M III −O−X (M I = Cu, Ag; M III = trivalent As, Sb, Bi; X = halogen) family.