Polycrystalline SrBi2Ta2O9 (SBT) ferroelectric thin films were prepared on Pt/Ti/SiO2/Si substrates by the metalorganic decomposition (MOD) technique. The dielectric properties of SrBi2Ta2O9 (SBT) capacitors were measured with HP4194 and RT6000HVS testers. The experimental results exhibited that the dielectric constant epsilon (r)(f) and ac conductivity sigma>(*) over bar * (f) of SET thin firms had a power law dependence on frequency. An increase in the ac conductivity with increasing frequency showed the relaxation of the leakage current of the SET capacitors in the first stage. The dielectric constant and ac conductivity were dependent on the thickness, temperature, grain size, and annealing ambient, etc. of the SET thin films.