We analyzed ferroelectric and paraelectric materials with a high dielectric constant, such as BaTiO3 (BT) ceramic, Ba1-xSrxTiO3 (BST) ceramic, SrTiO3 (ST) crystal and congruent LiTaO3 (CLT) crystal by THz time-domain spectroscopy (THz-TDS). We obtained the complex dielectric constants of BT ceramic, ST crystal, Ba0.20Sr0.80TiO3 ceramic and CLT crystal. The real and imaginary parts of the complex dielectric constant of the CLT crystal and ST crystal were in agreement with those previously reported. Furthermore, the real and imaginary parts of the complex dielectric constant of the paraelectric Ba0.20Sr0.80TiO3 ceramic were also obtained, and their values were similar to those of ST. As for the BT and BST ceramics, which are ferroelectric materials, we could characterize the real and imaginary parts of BT in the millimeter-wave region but not those of BSTs. We observed dielectric relaxation in BT at around 20 GHz in this measurement.