New electrospun (ES) sensory fibers consisted of poly(methyl methacrylate) (PMMA) core and ploy(3-hexylthiophene-2,5-diyl) (P3HT) shell were successfully prepared using a two-fluid coaxial electrospinning process. Field-emission scanning electron microscope (FE-SEM) studies showed that the prepared ES fibers had diameters of 500-700 nm and worm-like surface structure of P3HT on the fiber. Red emission fibers were exhibited from the laser confocal microscope. Upon exposed to air under light for two weeks, significant blue-shifting on both absorption and luminescence spectra was found on the prepared ES fibers. it was probably due to the chain scission occurred in the P3HT and led to the reduced conjugated length. The sensitivity of the ES fibers was much better than that of the spin-coated P3HT film from the comparison on the variation of photophysical properties. Besides, the EPR result indicated the formation of the P3HT center dot O(2) charge transfer complex (CTC), leading to the fiber conductivity of 10(-6) S/cm without an external doping. The present study demonstrates that conjugated polymer based ES core-shell fibers may have potential applications for oxygen-sensing devices.