MXenes with excellent conductivity and abundant surface functional groups have displayed great advantages as platforms for sensing materials. NiO also has drawn much attention for gas detection due to its unique merits of excellent catalytic activity. Herein, NiO nanoparticles are incorporated with multilayer Ti3C2Tx-MXene to develop excellent triethylamine sensors. Due to the larger specific surface area and formed p-p heterojunctions, the response of the NiO/Ti3C2Tx gas sensor is endowed with a response value of 950% to 50 ppm triethylamine gas and is much higher than that of the pristine NiO sensor. Moreover, the NiO/Ti3C2Tx sensor displays a fast response time of 8 s (50 ppm triethylamine), excellent reproducibility, and reliable long-term stability. This study proves that NiO/Ti3C2Tx sensors have potential for the effective detection of triethylamine gas.