PVP/WO3 hybrid nanofibers (NFs) are synthesized by embedding n-type semiconducting metal oxide WO3 nanoparticles (90-120 nm) in PVP NFs using electrospinning and their amperometric response is evaluated towards different concentrations of acetone. Material and structural properties of the PVP/WO3 hybrid NFs are characterized using SEM, FTIR, Raman and XPS. Amperometric responses of the PVP/WO3 hybrid NFs are investigated toward acetone as a function of bias voltages (3-7 V) without and with UV irradiation. The maximum response (1.42 mu A) was obtained at 7 V bias voltage for 12.5 ppm of acetone at operating temperature of 350 under photoexcitation with a rapid response/recovery time of 18s/42s. Detection of acetone down to 7 ppb at 7 V bias voltage under photo-activation is calculated. A possible sensing mechanism is also explained.