Electro-optic effects of PbZr0.52Ti0.48O3/PZT) and BaTiO3/BTO) ferroelectric thin films in the terahertz frequency range are studied with high-sensitive terahertz time-domain spectroscopy (THz-TDS).A linear response of PZT film with the linear electro-optic coefficient rc=6.73 × 10-11 m/V, and a quadratic response of BTO film with the second-order electro-optic coefficient Rc=l.42×l0-17 m2/V2, are observed at the frequency of 1 terahertz under the applied static electric field less than 80 kV/cm.The calculation of rc and Rc based on the Landau-Devonshire free energy theory explains the different electro-optic effects of PZT and BTO well.