(LaMn0.8Al0.2O3)1-x (Al2O3)x (0.05≤x≤0.2) negative temperature coefficient (NTC) ceramics were synthesized through a standard solid-state method. Thermogravimetry-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscope (EDS), resistance-temperature measurement and aging test were carried out to characterize the optimal calcined temperature, phase structure, morphology, elements concentration, R-T properties and electrical stability, respectively. The results show that the electrical resistivity of the ceramic samples increases remarkably as Al2O3 content increasing, while the constant B value has just little change. Specially, the ceramics exhibit superior properties of low B value (2816.44 K) and high resistivity (11893.89 Ω(cm) when x=0.15. In addition, the resistance variation (ΔR/R) of samples is less than 0.94% after aging at 125°C for 500 h.