This paper presents a feasible and efficacious procedure to synthesize polystyrene/upconversion nanocrystals (PS/UCNCs) nanocomposite spheres with raspberry-like structure via an in situ dispersion polymerization technique. During \this process, polyacrylic acid (PAA) as stabilizer plays the key role in adsorbing UCNCs, including NaYF(4):Yb(3+)-Er(3+), NaYF(4):Yb(3+)-Tm(3+) and NaYF(4):Yb(3+)-Ho(3+) onto the PS surfaces. TEM and SEM images confirmed the raspberry-like morphology of the obtained nanocomposite spheres. The effect of synthetic conditions, for instances, PAA amount, type and concentration of UCNCs on the structure and fluorescence of the PS/UCNCs nanocomposite spheres were studied in detail. (C) 2011 Elsevier Inc. All rights reserved.