Cesium salts of phosphotungstic acid Cs_xH_1−xPW₁₂O₄₀ were synthesized in the pH range of the initial solutions are from 0 to 4. It has been shown that the Keggin structure is preserved in the entire pH range without the presence of other anions. At pH = 2.0, there is a sharp change in the composition of the cationic sublattice, particle sizes, specific surface area of the obtained particles, and total pore volume. At these pH values, the size of the crystallites forming particles of the salts obtained remains almost unchanged with a change in pH. In the obtained compounds, water does not enter the salt structure and its content correlates with the pore size inside the particles. The dependences of proton conductivity, conductivity activation energy, and electrocatalytic properties of the obtained cesium salts can also be divided into two regions of pH influence with a transition of pH = 2.0.