The present invention provides a nano complex oxide doped dielectric ceramic material used for a multilayer ceramic capacitor using a base metal as a material of internal electrodes. The doped dielectric ceramic material comprises barium titanate and a nano complex oxide dopant, wherein the molar ratio of the barium titanate to the nano complex oxide dopant is in the range of (90 to 98):(2 to 10), the average particle size of the barium titanate is 50 to 300 nm and the nano complex oxide dopant has the following formula (1): wA+xB+yC+zD. The present invention also provides processes for preparing the nano complex oxide doped dielectric ceramic material and ultrafine-grained and temperature-stable multilayer ceramic capacitors using the nano complex oxide doped dielectric ceramic material as a material of dielectric layers.