Potassium antimony tartrate was synthesized by the solid-liquid phase reaction of antimony trioxide and potassium hydrogen tartrate. The composition and structure of the obtained complex had been characterized by element analysis, X-ray powder diffraction and infrared spectra. The results of indexes to the X-ray powder diffraction data indicate that the crystal structure of the potassium antimony tartrate belongs to monoclinic system. The lattice parameters are: a = 0.8250 nm，b = 1.6046 nm，c = 1.7736 nm，β = 96.65°. The synthetic conditions were found as following: the molar ratio of antimony trioxide, potassium hydrogen tartrate and water was 1.05 : 2.0 : 92, the temperature of reaction was 90 °C, the reaction time was 4.5 h, the product yield of reaction was 86.8%.