The field emission properties of SnO2 nanowires fabricated by chemical vapor deposition with metallic catalyst-assistance were investigated. For the as-fabricated SnO2 nanowires, the turn-on and threshold field were 4.03 and 5.4 V/μm, respectively. Considerable enhancement of field emission of SnO2 nanowires was obtained by a post-annealing process in oxygen at high temperature. When the SnO2 nanowires were post-annealed at 1,000 °C in oxygen, the turn-on and threshold field were decreased to 3.77 and 4.4 V/μm, respectively, and the current density was increased to 6.58 from 0.3 mA/cm2 at the same applied electric field of 5.0 V/μm.