As a typical two-dimensional (2D) layered transition metal dichalcogenides (TMDs), tungsten disulfide (WS2) has been considered as a promising sensing material for room-temperature NH3 detection. However, the bulk WS2 based room-temperature NH3 sensors can hardly recover to its initial state after turning off gas. Although the recovery rate of bulk WS2 was accelerated by thinning method, the response of few- or monolayer WS2 nanosheets (NSs) to NH3 was sharply decreased. Here, in premise of keeping fast recovery rate, few- or monolayer WS2 NSs modified with Pt quantum dots (QDs) were prepared for room-temperature NH3 detection, which exhibited significantly enhanced sensing properties with fast recovery speeds. Especially, the response of nanocomposite to 250 ppm NH3 is nearly 10 times than that of WS2 NSs, which could be attributed to the significantly decreased initial conductivity caused by electrons flowing from higher Fermi level of Pt QDs to that of WS2 NSs and the higher catalytic activity. Furthermore, the Pt-S bonds confirmed by XPS results could benefit electrons transfer between the interface. We hope that the 0D/2D heterostructure system in this work could provide a direction to improve sensing properties of 2D TMDs-based room-temperature sensors.