Abstract: The structure and dielectric properties of the BaO-TiO2-Nd2O3-La2O3(BTNL)system are investigated in this paper. BTNL system is the result of La2O3 partly replacing Nd2O3 in the BaO-TiO2-Nd2O3(BTN) system. By analyzing XRD diffractogram, it is proved that the temperature coefficient ((decreases with the increase of molar ratio of La2O3 and Nd2O3, because of the increase of the crystalline phases of BaLa2Ti4O12 and La2Ti2O7. Adding proper quantities additions into the BTNL system, the microwave ceramic material with ultra low loss can be achieved sintered at middle temperature, which can be used to prepare microwave monolithic capacitor.