Hollow nanocapsules with both photoswitchable-fluorescent and reversible-photochromic properties are synthesized via a one-pot non-templating microemulsion copolymerization using methyl methacrylate and methacrylated spiropyran as co-monomers. The strong photoswitchable fluorescence of the nanocapsules are switched between "on" and "off" by alternating irradiation of ultraviolet and visible light, which causes the reversible photoisomerization between spiropyran and merocyanine in the nanocapsules. The distribution of spiropyran/merocyanine in a nanocapsule is mostly incorporated inside the wall of the nanocapsule, with only about 17.7% on the surface of the wall. This confinement is the reason of the unusually strong fluorescence of the merocyanine form yielded by the UV radiation. For the same reason. the photochemical stability of the chromophores is increased compared to those in the solution of water/DMF mixture. (C) 2009 Elsevier Inc. All rights reserved.