The crystals Gd2SiO5 and Yb-doped Gd2SiO5 were grown by Czochralski method successfully. Dielectric properties of the two crystals were investigated in the temperature range from 100 to 1100K and the frequency range from 20Hz to 10MHz. Our results revealed that these crystals show intrinsic dielectric behavior in the temperature below room temperature, whereas in above room temperature, a relaxor-like dielectric anomaly and a metal-insulator transition were observed. It was found that the relaxor-like anomaly contains two dielectric relaxations. Impedance analysis showed that the low- and high-temperature relaxations are dipolar- and Maxwell-Wagner-type relaxation, respectively. The transition was found to be strongly related to oxygen vacancies, which leads to positive temperature coefficient of resistance and an abnormal dielectric behavior contrary to the conventional thermally activated behavior at temperatures near the transition temperature.