Polyaniline/titanium dioxide (PANI/TiO(2)) composite nanofibers were prepared by combining the electrospinning technique with chemical oxidation polymerization. Firstly, Mn(3)O(4)/TiO(2) nanofibers were prepared by electrospinning, and then the Mn(3)O(4) in the Mn(3)O(4)/TiO(2) nanofibers acted as an oxidant to oxidatively polymerize aniline. As a result, Mn(3)O(4) was completely consumed while PANI/TiO(2) composite nanofibers were formed. The gas sensors of the composite nanofibers with different PANI to TiO(2) ratios were fabricated on home-made gold electrodes, and the sensing property for ammonia gas detection was investigated at room temperature. Results showed that the composite nanofiber sensor could detect as low as 25 ppb ammonia gas, which is superior to the PANI nanofiber without TiO(2) nanoparticles. The sensing sensitivity of the composite nanofibers strongly depends on the ratio of PANI to TiO(2). The mechanism of sensitivity enhancement of the PANI nanofiber sensors mixed with TiO(2) nanoparticles was also discussed. (C) 2011 Elsevier B.V. All rights reserved.