The terbium complex Tb(acac)(2)AA (acac: acetyl acetone, AA: acrylic acid) was incorporated into polystyrene (PS) matrix and electrospun into various composite fibers. The mass ratios of rare-earth complex to polymer were fixed in all composite fibers. The diameters of the composite fibers decrease with increase in the collection distance during electrospinning. The luminescence properties of the Tb(acac)(2)AA/PS composite fibers were studied in comparison to those of the pure Tb complex. The excitation bands became narrower and blue-shifted compared with that of the pure complex in all of the Tb(acac)(2)AA/PS composite fibers. The fluorescence lifetime of the D-5(4) state of Tb3+ ion in the composite fibers was shorter than that of the Tb complex. The effect of the fiber diameter on the luminescence properties was also studied. As a result, the fluorescence lifetimes of the D-5(4) state in all of the Tb(acac)(2)AA/PS composite fibers decreased gradually with decrease in diameter.