Carbonization followed by calcination in air has been developed to synthesize porous SnO₂based nanofibers. The precursor nanofibers were synthesized through electrospinning. The optimal synthesized condition was investigated according to the gas sensing properties of pure SnO₂nanofibers through adjusting the heating rate in air. Gas sensors based on 1% Pd doped SnO₂nanofibers under this optimal synthesized condition were fabricated, and the gas sensing properties was systematically investigated. The experimental results indicate that all the carbonized nanofibers have a porous microstructure. For the pure SnO₂nanofibers, carbonized nanofibers also have a hollow structure. At the optimal synthesized condition, the sensor based on the carbonized SnO₂nanofibers Exhibits 2.6 times higher response (20.4) than pristine pure SnO₂nanofibers (7.7) toward 100 ppm ethanol. However, the selectivity is almost unchanged. For the Pd doped SnO₂nanofibers, the gas response is improved from 10 to 24.6 to 100 ppm toluene at optimum operation temperature under the carbonization process. The sensors also exhibit a low detecting limit (1.6-500ppb toluene) and a short response time (similar to 3s). The evolution process and the formation mechanism were also discussed.