Ultrathin polypyrrole (PPy) films with the thicknesses of 20, 50, and 100 nm were prepared by electropolymerization. Co particles with a charge density in the range of 125-1,250 mC cm(-2) were grown on these ultrathin PPy films. Current time transients were used to investigate the electrochemical properties. It was observed that the deposition of Co becomes more difficult as the PPy film gets thicker. The chemical structure of PPy films in the reduced and oxidized forms and a PPy film with Co particles were examined with Fourier transform infrared spectroscopy (FTIR). The characteristic peaks of the oxidized PPy film were observed. The intensity and position of some peaks changed, and new peaks appeared for the reduced PPy film, possibly as a result of undoping of the PPy film. There are further differences in the spectrum of Co on PPy. The morphology of the films was studied by scanning electron microscopy (SEM). It was found that the morphology was affected by both the PPy film thickness and the Co charge density. Magnetic measurements were made by vibrating sample magnetometry (VSM). The magnetic moment of the samples increases with both decreasing PPy film thickness and increasing charge density due to increased Co deposition.