Dielectric properties of solution-gas interface-formed Fe(OH)₃ thin-film capacitors (Al/Fe(OH)₃/Al) of various thicknesses have been studied in the frequency range 10–10⁶ Hz at various temperatures (300–443 K). Dielectric constant, ε, increases with increasing film thickness (d) and temperature (T) and decreases with increase of frequency (f). The loss factor (tan δ), showing pronounced minimum with frequency, increases with rise of temperature, and tan δ_min shifts to a higher frequency. The large increase in dielectric constant towards low frequency region indicates the possibility of an interfacial polarization mechanism in this region.