The frequency-dependent impedance/dielectric behavior of the brick-layer model (BLM) was investigated vs. grain size and local parameters (resistivity, dielectric constant, and grain boundary width). The simulation shows a maximum in capacitance vs. grain size, governed by the grain boundary-to-grain interior resistivity ratio. The BLM was employed to analyze the 500 °C impedance behavior of polycrystalline cerium dioxide from the nano- (∼15 nm grain size) to the micro- (∼4 μm grain size) regime. The grain boundary resistivity is orders of magnitude larger than that of the grain interiors in the microcystalline specimen. This contrast is significantly smaller in the nanocrystalline specimens, suggesting enhanced conduction at grain boundaries. The limitations of the BLM for simulating the behavior of complex electroceramic microstructures are discussed.