CeO2-decorated SiO2/PANI free-standing nanofibrous membranes were fabricated using an approach which involved electrospinning-electrospraying, calcination and in situ polymerization. Specifically, the CeO2 precursor deposition on the electrospun nanofibers surface was done through electrospraying, followed by the calcination which resulted in CeO2 particles and SiO2 free-standing nanofibers. By incorporating CeO2, ammonia sensing properties of the as-prepared SiO2/PANI free-standing composite nanofibers (SiO2/PANI FCN) can be dramatically improved. The sensing response value of SiO2/CeO2/PANI free-standing composite nanofibers (SiO2/CeO2/PANI FCN), analyzed with 300ppm ammonia, was ca. 36.98, which was superior to SiO2/PANI composite nanofibers. The ammonia sensing mechanism of the SiO2/CeO2/PANI FCN can be attributed to the P-N heterojunctions formed between p-type PANI and n-type CeO2. Furthermore, the SiO2/CeO2/PANI free-standing ammonia sensor presented ideal selectivity and repeatability. This work provided a new insight into the development of free-standing and high-performance gas sensors.