Eu(OA)3(TTA) (OA=cis-9-octadecenoic acid, TTA=4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione) complexes (Eu- complexes) containing the ligand OA with long molecular chains were synthesized. The Eu(OA)3(TTA) complexes and peroxide were added into nitrile-butadiene rubber (NBR) by mechanical shearing to get the uncured composites. The cured composites were obtained by vulcanizing the uncured composites at high temperature. The in-situ reaction including polymerization and grafting of Eu-complex took place at the curing process, which was verified by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations showed the fine dispersion of Eu(OA)3(TTA) complex (Eu-complex) in the cured composites compared with the uncured ones. Fluorescent spectra and Judd-Ofelt parameters analysis revealed that the fluorescent intensity increased approximate linearly with the content of Eu- complex increasing due to the in-situ reaction and long molecular chains of OA. The fluorescent lifetime of composites was longer than that of original Eu-complexes. (OA = cis-9-octadecenoic acid, TTA = 4,4,4-trifluoro-1- (2-thienyl) -1,3-butanedione) complexes ligand OA with long molecular chains were synthesized. The Eu (OA) 3 (TTA) complexes and peroxide were added into nitrile-butadiene rubber (NBR) by mechanical shearing to get the uncured composites. The cured composites were obtained by vulcanizing the uncured composites at high temperature. The in-situ reaction including polymerization and grafting of Eu-complex took place at the curing process, which was verified by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) and transmission electron microscopy (TEM) observations showed the fine dispersion of Eu (OA) 3 (TTA) complex (Eu-complex) in the cured composites compared with the uncured ones. Fluorescent spectra and Judd-Ofelt parameters analysis revealed that the fluorescent intensity increased approximate linearly with the content of Eu-complex in creasing due to the in-situ reaction and long molecular chains of OA. The fluorescent lifetime of composites was longer than that of original Eu-complexes.