Quantitative determination of Arsenic acid by precipitation of Arsenic acid as ZnNH$_{4}$AsO$_{4}$ and titration of Zn in the precipitate by EDTA has been investigated. Conclusion are as follows; 1) ZnNH$_{4}$AsO$_{4}$ was Soluble in NH$_{4}$Cl-NH$_{4}$OH buffer solution of pH lo and back-titration was unnecessary as in the case of MGNH$_{4}$AsO$_{4}$. 2) The end point was clear whether AsO$_{4}$$^{-3}$ present or not. 3) More simple and rapid method than that of Gravi metric method. 4) Could be determined within 0.3% error.