The crystal structure of KSbMo2O8 was determined from single-crystal X-ray diffraction data. It crystallizes in the triclinic space group P1 with a = 5.015(2), b = 7.4216(6), c = 10.304(1) Å; α = 90.45(1), β = 100.29(2), γ = 107.79(1)°; V = 358.5 Å3, Z = 2, R = 0.028, Rw = 0.038 for 1590 unique reflections with I > 2.5 σ(I). The structure contains layers of antimony molybdate with the potassium cations between the layers. Each layer is built up from strongly distorted MoO6, MoO5, and SbO6 polyhedra and consists of two types of chains parallel to the a-axis. Sb2O10 dimers, formed by two edge-sharing SbO6 polyhedra, are connected by MoO5 groups to form chains. The other type of chains is constructed from skew edge-shared MoO6 octahedra, which are linked through Sb2O10 dimers such that layers in the (010) plane are formed. Each K+ cation is coordinated by nine oxygen atoms in a geometry of tricapped trigonal prism.