In this work, the mixed-potential-type gas sensor based on NASICON solid electrolyte and MMnO3 (M: Gd, Sm,La) sensing electrode (SE) was developed and fabricated aiming at the low-concentration triethylamine (TEA) detection. The research point of the fabricated sensors mainly concentrated on the effect of different A-site elements in MMnO₃-SE (M: Gd, Sm, La) on TEA sensing characteristics. The result reveals that the highest response value (−217.5 mV) towards 50 ppm TEA was observed for the device utilizing SmMnO3-SE. The highest electrochemical catalytic activity of the fabricated sensors attached with SmMnO₃-SE was further au thenticated by the polarization curve measurement. Moreover, the response value displays a segmentally linear relationship with TEA concentrations and the logarithm of TEA concentrations, and the slopes are −49 mV/ppm and −105 mV/decade at the ranges of 0.05–0.5 ppm and 1–50 ppm TEA, respectively. The device could also produce an acceptable response value (−5.6 mV) towards 50 ppb TEA. Moreover, it also displays good re peatability and selectivity, along with steady response signals towards 5 ppm and 50 ppm TEA for 15 days and 1 ppm TEA at different humidity levels.