A ceramic sample of a layered cuprate of Tl2Ba2Ca2Cu3Ox and Tl2Ba2Ca1Cu2Ox, so-called Tl-based 2223 and 2212 compounds, was investigated by the measurement of the dielectric constants (epsilon' and epsilon"), the dielectric loss (tan 6), and the conductivity (sigma(ac)) as a function of temperature (80-300 K) and frequency (100 Hz-10 MHz). A negative capacitance phenomenon has been observed and it is believed that the negative capacitance effect is due to the polarization effect. The negative dielectric constant has been calculated from the negative capacitance. The dielectric constant (epsilon') and the dielectric loss (tan delta) show strong dispersions at lower frequencies. The dielectric properties of the sample were found to have strong frequency and temperature dependence.