The effects of (Na0.5Bi0.5)TiO3 (NBT) and MgO addition on the dielectric properties and microstructures of BaTiO3 (BT) ceramics were investigated. NBT was first added to Nb2O5-doped BT system. As NBT content increases from 0 to 0.2 mol, the Curie temperature of the systems shifts to high temperatures and dielectric constant peak at T (c) is suppressed evidently. The variation of capacity (Delta C/C (20 A degrees C) (%)) of the system at 200 A degrees C decreases with increasing NBT content from 0.1 to 0.2 mol, but that of -55 and 125 A degrees C increases monotonously. The stable temperature characteristics of the dielectric properties improved by NBT doping would be connected with the distortion and deformation of the structure induced by substitution of Na+ and Bi3+ into Ba sites. MgO was employed to further flatten the Delta C/C (20 A degrees C)-T curve. It is very helpful for this ceramic system to satisfy the requirement of EIA-X9R specification on Delta C/C (20 A degrees C) and still keep a satisfied dielectric constant. The addition of MgO improved effectively the temperature stability of the dielectric properties. Changes of the crystalline structure and microstructure induced by MgO doping might contribute to these improvements.