A new kind of precipitate, antimony arsantimonate, was found during the precipitation reactions in acidic solution containing As(Ⅲ), Sb(Ⅲ) and Sb(Ⅴ) by means of chemical analysis, SEM, XRD and IR spectrometry. The results show that the As content in antimony arsantimonate increases with the increase of n(As(Ⅲ))/n(Sb) in solution and the content of component Sb(Ⅲ) and Sb(Ⅴ) remains almost constant with the variation of n(Sb(Ⅲ))/n(Sb(Ⅴ)) in solution. The antimony arsantimonate is a kind of floccules with size of 1-5 μm. The crystal performance of the compound gets better with the decrease of n(As(Ⅲ))/n(Sb), the cell parameter of which is near to 10.33 × 10-10 m under different n(As(Ⅲ))/n(Sb) and As atom locates on the surface, not in the inner of the grain. The chemical bonds of As-OH, Sb-OH, As-O-Sb, Sb-O-Sb and O-H of the precipitate are included in the precipitate. The chemical structure of precipitate is described as Sb(OH)2-O-[Sb(OH)3-(O-As(OH)-O-Sb(OH)3.3]-O- arsantimonate precipitate forms.