The electrochromic response of the Prussian blue (PB) system is produced by the electrochemical reaction of the colourless Everitt’s salt (ES), K2FeFe(CN)6, to form the blue oxidation product, KFeFe(CN)6. Reviews on the electrochemistry of PB and related compounds are available. Very little work, however, has been published on the quantitative aspects that affect film stability. The reported electrochemical deposition conditions for PB film formation vary considerably in terms of the electrochemical technique, pH, ferricyanide concentration, supporting electrolyte, as well as composition and concentration of the iron (III) salt. In this study, most PB films were prepared at ambient temperature from acidic K2SO4/H2SO4 (pH ≅ 2.0) solutions containing either Fe(ClO4)3 or FeCl3 and K3Fe(CN)6, using potentiostatic conditions. Dramatic increases in the film stability are obtained by simple acidifying; in fact, the switching speed increased from about 2 seconds at a pH of 7 to about 0.2 seconds at a pH of 2. Cycle lifetimes of at least 100,000 cycles were obtained in all of the acidified solutions. Factors such as the solution pH and heat treatment of the PB film also affect the position and shape of the observed cyclic voltammetric peaks. Summarizing, the PB films prepared by an electrodeposition method appear to be very promising for reaching stable, reversible and fast switching time (2 Hz) materials.