This paper demonstrates chemi-resistive type and QCM ammonia sensors based on Ti3C2Tx MXene with surface engineering. The morphology and structure composition of Ti3C2Tx MXene were completely tested by XRD, SEM, TEM and Raman. The ammonia sensing performance of Ti3C2Tx MXene sensors at room temperature were systematically studied. The QCM sensors show better performance towards ammonia than chemi-resistor sensors. The Ti3C2Tx-S QCM sensor possesses quite sensitivity (49 Hz@100 ppb), high response/recovery capability (33 s/58 s) and good selectivity. XPS was introduced for the surface element status for the potential ammonia adsorption mechanism. It can be mainly related to for lowest average potential for reaction of Ti-S and the additional absorption towards the product nitric oxides enhancing the frequency shift by absorption mass increasing. This work confirms that surface engineering of Ti3C2Tx MXene to be effective method for enhancing gas sensing performance, and the sensor shows potential application for low concentration ammonia sensing. Display omitted •Treated Ti3C2Tx MXene was fabricated via surface engineering with simple solution process.•Chemi-resistance type and QCM gas sensors were fabricated by spin coating method without further treatment.•Ti3C2Tx-S QCM sensors exhibited excellent performance for ammonia gas detection and detection limit was down to 10 ppb.•Potential ammonia absorption and electronic sensing mechanism of surface medicated Ti3C2Tx MXene was discussed.