The growth behavior of nanograins in CuO nanofibers was investigated. The apparent activation energy for the growth of nanograins is estimated to be similar to 18 kJ/mol, which is smaller by one order of magnitude compared with those of bulk oxide ceramics. The isothermal grain growth behavior exhibits the lattice diffusion in a pore control scheme as a main growth mechanism. The sensing properties of the sensors fabricated with the CuO nanofibers have been investigated in terms of CO and NO2. Importantly, the sensitivity of the sensor fabricated with CuO nanofibers having larger nanograins is much higher than that of the sensor with smaller nanograins. The results suggest not only that the electrospinning-synthesized p-type CuO nanofibers hold promise for realizing sensitive and reliable gas sensors, also that calcination conditions need to be optimized to obtain the best sensing properties. (C) 2011 Elsevier B.V. All rights reserved.