The processes involved in the formation of the positive lead‐acid battery plate in with sp gr 1.15 and 1.05 and in 0.7M were studied by x‐ray diffraction, wet chemical analysis, and microscopic observations. It was found that formation takes place in two stages. During the first one, and penetrate from the bulk of the solution into the plate. As a result of chemical and electrochemical reactions and basic sulfates of lead are converted to and . These compounds form zones which advance into the paste. Part of the hydrogen ions evolved during the reaction of formation of migrate from the plate in order for the latter to remain electroneutral. During the second period is consumed in the plate. Lead sulfate is oxidized to . Sulfuric acid originates and diffuses in a direction opposed to that in the first period. Taking into account specific conditions of the chemical and electrochemical reactions in porous electrodes a mechanism is suggested for the formation processes of the positive plate. Ion diffusion and migration are considered to be the rate‐limiting steps of the processes. The direction of advance of the and zones is explained in terms of this mechanism as well as the ratio during formation in the three solutions. The parameters which control the phase composition of the active material of the lead‐acid battery positive plate are listed.