Rapid detection of n-pentanol is of great significance. Herein, we presented an excellent n-pentanol gas sensor based on bimetallic PtAu alloy nanocrystals (NCs) modified flower-like WO3. PtAu NCs with relatively uniform size were synthesized through a reduction method in oleylamine solution. The sensitive materials of flower-like WO3 with different mass percentages of PtAu NCs were prepared by impregnation. WO3 with the loading amount of 0.5 wt% showed a response of 162 (Ra/Rg) for 20 ppm n-pentanol at 200 °C, which was 105 times higher than that for pure WO3. PtAu adding enhanced the response due to the sensitization and their synergistic effect. It is noteworthy that PtAu-modified WO3 exhibited ultrafast response/recovery speed (tres = 1 s, trec = 3 s) to n-pentanol, as far as we know it is the fastest n-pentanol sensor based on semiconductor until now. Flower-like WO3 3D nanostructures allow fast diffusion of gas molecules, resulting in the high rates of gas adsorption and desorption. At the same time, with the help of the bimetal catalysis, the reaction was further promoted. This work can provide a new solution strategy for fast detection and real-time monitoring of n-pentanol in chemical plants.