The speciations of antimony and arsenic in the Neoproterozoic-Cambrian strata in western Hunan have been studied with partial dissolution techniques. In rocks, Sb and As have four modes of occurrence: exchangeable, bound to sulfides, bound to carbonates and in silicate mineral lattice. The average percentages of the four fractions of antimony are 18. 65% , 0. 85% , 31. 41% and 43. 81%, respectively, and the average percentages of the four fractions of arsenic are 7. 05%, 4. 29%, 56. 11% and 29. 18%, respectively. The movable fractions of antimony and arsenic are 55. 91% and 67. 45%, respectively. The leaching rates of elements in the open sulfur-bearing system are approximately proportional to the percentages of movable fractions, which furnishes experimental evidence for the existence of source beds of antimony and arsenic in the region.