Novel cellulose acetate (CA)/polyethylenimine (PEI)/poly(acrylic acid) (PAA) nanofibers/quartz crystal microbalance (QCM) sensor was successfully fabricated for ammonia gas detection in this study. The morphology and chemical property of as-prepared nanofibers were characterized using field emission scanning electron microscopy (FE-SEM) and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). Gas sensing test showed that incorporated into QCM system, the CA/PEI/PAA nanofibers exhibited an outstanding and desirable sensing behavior, including high sensitivity, fast response and good repeatability, making them a promising candidate as an ammonia gas detector.