The ac impedance behaviour of electrochemically grown dendritic Ag three-dimensional electrodeposits grown from aqueous Ag₊ ion containing solutions has been studied in the blocking regime covering the 1 ⩽ f ⩽ 10₄ Hz frequency range (ω = 2πf). These deposits exhibit fractal surface and non fractal mass (volume) characteristics. Impedance data displayed as log Z″ vs. log ω plots show two linear portions with different frequency dispersion exponents <α > = 0.95 ± 0.03 and <α > = 0.67 ± 0.05, respectively. The crossover frequency, ω_λ, as determined from those plots, mainly depends on the electrolyte resistivity and, to a minor extent, on the Ag₊ ion electrodeposition charge. For ω > ω_λ, the surface fractal dimension derived from the reciprocal relationship, D_s = (1/α) + 1, is D_s = 2.45 ± 0.1. This figure agrees with that obtained from the log (area) vs. log (volume) plots.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas