Yttrium-doped CaCu(3)Ti(4-x)Y(x)O(12-x/2) (x=0-0.1) samples were fabricated by using solid-state sintering, and their electric and dielectric properties were investigated. Yttrium addition has shown to reduce the dielectric loss remarkably while maintaining colossal permittivity. At x=0.5, the loss (tan delta) is below 0.1 over the frequency range from 1 to 300 KHz, while that of the pure ceramic is above 0.1 over most measuring frequency range. The current density-electric field curves proved that yttrium doping can effectively enhance the varistor voltage, indicating a rise of the potential barrier height at the grain boudaries. Local measurement of impedance at the grain boundaries was performed by using microcontact probes. The results indicated that yttrium dramatically increases the resistance of the grain boundaries. The differences are attributed to the enhanced Cu segregation at grain boundaries, which is induced by yttrium doping.