High-temperature stability and reliability are in high demand for ultra-thin multilayer ceramic capacitors (MLCCs), which are ubiquitous in electronic industries. Here, two doping matrices of BaTiO₃ (BT) and Ba_0.97Ca_0.03TiO₃ (BCT) are chosen to prepare ultra-thin MLCCs, whose effects on the microstructure, nonlinear dielectric properties, temperature stability, and reliability of the capacitors were investigated. Compared with BT-based MLCCs, BCT-based MLCCs possess better core-shell structures, thus, leading to a higher Schottky barrier for inhibiting carrier migration and improving aging performance. For the 1.5 μm-thickness capacitors using the BCT doping matrix rather than BT, the temperature coefficient of capacitance reaches the X7R standard, and the breakdown field increases from 148 to 172 V/μm. Moreover, the ability to resist insulation resistance degradation has been significantly improved. This work demonstrates the great potential of using BCT as the doping matrix to prepare ultra-thin MLCCs with excellent temperature stability and reliability.