Er3+ doped BaYF5 nanofibers have been successfully fabricated by electrospinning combined with a double-crucible fluorination method we recently proposed. For the fabrication process, the first step is to prepare PVP/[Ba(CH3COO)(2) + Y(NO3)(3) + Er(NO3)(3)] composite nanofibers via electrospinning, the next step is calcining the composite nanofibers into mixed oxide nanofibers in air, and finally BaYF5:Er3+ nanofibers are successfully synthesized by fluorination of the as-prepared mixed oxide nanofibers used as precursor via a double-crucible method applying NH4HF2 as fluorinating agent. X-ray diffractometry analysis reveals that BaYF5:Er3+ nanofibers are pure tetragonal phase with space group of P/421m. The diameter of BaYF5:Er3+ nanofibers is 109.9 +/- A 10.9 nm under the 95 % confidence level. Upconversion emission spectra analysis manifests that BaYF5:Er3+ nanofibers emit strong green and weak red upconversion emissions centering at 522 (H-2(11/2) -> I-4(15/2)), 540 (S-4(3/2) -> I-4(15/2)) and 651 (F-4(9/2) -> I-4(15/2)) nm, respectively. Moreover, the emitting colors of BaYF5:Er3+ nanofibers are located in the green region in CIE chromaticity coordinates diagram. The optimum doping molar concentration of Er3+ ions is found to be 5 %. The formation mechanism of the BaYF5:Er3+ nanofibers is also studied. This preparation technique can be applied to fabricate other rare earth fluoride nanofibers.