[Display omitted] • Ti 3 C 2 T x /WO 3 was synthesized successfully with facile ultrasonication techniques. • The response of Ti 3 C 2 T x /WO 3 -50% to 1 ppm NH 3 is 15.4 times higher than Ti 3 C 2 T x. • The heterojunction plays a vital role on the enhancement of sensing performance. Low-power consumption and high sensitivity are highly desirable for a vast range of NH 3 sensing applications. As a new type of two-dimension (2D) material, Ti 3 C 2 T x is extensively studied for room temperature NH 3 sensors recently. However, the Ti 3 C 2 T x MXene based gas sensors suffer mainly from low sensitivity. Herein, we report a sensitive Ti 3 C 2 T x /WO 3 composite resistive sensor for NH 3 detection. The Ti 3 C 2 T x /WO 3 composite consisting of WO 3 nanoparticles anchored on Ti 3 C 2 T x nanoflakes were synthesized successfully with a facile ultra-sonication technique. The composite sensor with optimized components exhibits a high sensitivity of 22.3% for 1 ppm NH 3 at room temperature, which is 15.4 times higher than the pure Ti 3 C 2 T x sensor. Furthermore, the composite sensor has excellent reproducibility, good long-term stability, and high selectivity to NH 3. The relative humidity influence on NH 3 gas sensing properties of the sensors was systematically studied. This research provides an efficient route for the preparation of novel MXene-based sensitive materials for high-performance NH 3 sensors. [ABSTRACT FROM AUTHOR]