The potentiostatic synthesis and microgravimetric kinetics of hybrid materials polypyrrole/PW12O403- has been investigated. Every electrogenerated film was controlled by cyclic voltammetry. Charge consumed during polymerization, weight of the electrogenerated films, charge stored in the film, weight of the film after charge/discharge cycles, productivity of the electropolymerization charge (mg mC(-1)) and specific charge (mA h g(-1)) stored in the material were obtained for every film. The influence of the variables potential of polymerization, pyrrole or polyoxometalate concentrations, temperature, arid polymerization time was studied. Whatever the conditions of synthesis, a constant productivity of 1.9 x 10(-3) mg mC(-1) was obtained. Every electrogenerated film undergoes a weight loss up to 80% during the initial cathodic voltammetric control. The insoluble part of the films electrogenerated at increasing potentials stores an almost constant specific charge near 100 mA, h g(-1), showing that increasing rates of degradation processes, usually found in other electropolymerization processes, are not present in this system. The high reaction order of the kinetics related to the polyoxometalate concentration was attributed to the formation of adducts polyoxometalate-pyrrole, adducts being the electroactive species during electropolymerization. Results show that the mechanism of the electropolymerization process does not change in a significant way when the conditions of synthesis are changed.