The effects of La concentration on the electrical conductivity and electric modulus of Y2/3-xLaxCu3Ti4O12 ceramics (0.00x0.20) were investigated in detail. Proper amount of La substitution in Y2/3-xLaxCu3Ti4O12 ceramics made the dielectric loss decreased. When x=0.10, Y2/3-0.10La0.10Cu3Ti4O12 ceramics exhibited the highest grain-boundary resistance (0.893M) and the lowest dielectric loss (about 0.025 at 1kHz), meanwhile the samples exhibited a relatively high dielectric constant above 6000 over a wide frequency range from 40Hz to 1MHz. The decreased dielectric loss was attributed to the enhanced grain-boundary resistance. With the increase in La concentration, the dielectric relaxation behaviors correlated with the grain-boundary effects were significantly enhanced. By La doping, the activation energies for the conduction in grain boundaries were slightly depressed, and the activation energies for the relaxation process in grain boundaries were slightly changed. Based on the activation values, it can be concluded that the doubly ionized oxygen vacancies V-O(center dot center dot) had substantial contribution to the conduction and relaxation behaviors in grain boundaries.