The microstructure and dielectric properties of a SrTiO3-based GBL (Grain Boundary Layer) capacitor were investigated. The 0.6 mol% Nb2O5 doped SrTiO3 was sintered for 3 hr at 1450$^{circ}C$ in mixed gas(N2/H2) atmosphere. The Nb2O5 promoted the grain growth of the SrTiO3 ceramics was decreased with the amount of Nb2O5. The oxide mixture(PbO, Bi2O3, B2O3) were painted on the reduced specimen and fired at 1000$^{circ}C$ to 1100$^{circ}C$ in air. The penetrated oxide mixture into specimen were located in grain boundaries. A SrTiO3-based GBL capacitor had the apparent permittivity of about 3.0${ imes}$104, the dielectric loss of 0.01-0.02, and insulating resistance of 108-109$Omega$.cm. The capacitor had the stable temperature coefficient of capacitance and exhibited dielectric dispersion over 107 Hz. The capacitance-voltage measurements indicated that the grain boundary was composed of the continuous insulating layers.