Different concentrations of bis-beta-diketonate complex Eu-2(BTP)(3)(Phen)(2) (BTP = 1,3-bis(4,4,4-trifluoro-1,3-dioxobutyl)-phenyl and Phen = 1,10-phenanthroline) were doped into the poly(methylmethacrylate) (PMMA), forming a series of red Eu/PMMA luminescent nanofibers, via electrospinning technology. Various characterization techniques were employed to reveal the effect of Eu-2(BTP)(3)(Phen)(2) on the morphology, thermal stability, and luminescence of composite nanofibers. FT-IR spectra show the Eu-2(BTP)(3)(Phen)(2) complex was successfully doped into PMMA. The luminescent spectra of the composite nanofibers show strong characteristic emission of Eu3+ ions. Simultaneously, in comparison with the precursor complex Eu-2(BTP)(3)(Phen)(2), the Eu/PMMA nanofibers has a great improvement in thermal stability. Furthermore, the Judd-Ofelt theory and simulative constructions of the complex are employed to explain the effect of the dispersion of Eu-2(BTP)(3)(Phen)(2) and the interactions between the Eu-2(BTP)(3)(Phen)(2) complex and neighboring chain segments of PMMA.