A simple and effective solvent swelling method was developed for the preparation of poly(methyl methacrylate) (PMMA)/europium (Eu) complex hybrid nanospheres. Transmission electron microscopy and dynamic light scattering results indicate that the as-prepared PMMA-Eu nanoparticles had a spherical morphology, with a narrow particle size distribution ranging from 100-200 nm. The PMMA-Eu nanospheres exhibited strong red emissions with a maximum peak at 612 nm under UV excitation, and the luminescence lifetime of the Eu complex was enhanced after it was swollen into PMMA nanospheres. Furthermore, the luminescence intensity of the PMMA-Eu nanospheres was very stable in various severe media, including aqueous solutions with various pHs, 1 mM Ca2+, 1 mM Fe2+, 1 mM Cu2+, 0.1M phosphate-buffered saline solution, 1 mM citric acid solution, 1 mM lysine, and 1 mM glutamic acid. After the nanospheres were incubated at various temperatures for 1 h, the luminescence properties remained stable when the temperature was less than 40 degrees C yet decreased slightly between 40 and 60 degrees C and decreased rapidly at higher temperatures. These luminescent nanospheres were successfully applied in the luminescence-sensing assay of hydrogen peroxide and exhibited a high sensitivity and broad linear concentration range. Because of their unique luminescence properties, the as-synthesized PMMA-Eu nanospheres are expected to have great potential for use as luminescent labels or probes for long-time imaging and analysis in which severe media situations are present. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 128: 845-850, 2013