In this work, crystalline mesoporous-assembled ZrO2 nanoparticles were synthesized by a facile sol-gel process with the aid of a structure-directing surfactant. In order to investigate their physicochemical properties, the XRD, N-2 adsorption-desorption, pore size distribution, UV-visible spectroscopy, SEM, and TEM analyses were performed. The characterization results revealed the high crystallinity and uniform particle size of the synthesized mesoporous-assembled ZrO2 nanoparticles. Their mesopore size distribution was very narrow and monomodal. Based on the characterization results, a possible mesopore formation model of the mesoporous-assembled ZrO2 nanoparticles was proposed. The photocatalytic Methyl Orange (MO) dye degradation performance of the synthesized mesoporous-assembled ZrO2 nanoparticles under UV light irradiation was also evaluated as compared with that of the commercial P-25 TiO2 powder. It was found that the synthesized mesoporous-assembled ZrO2 nanoparticles exhibited a comparatively higher MO degradation activity than the commercial P-25 TiO2 under identical optimum conditions. (C) 2013 Elsevier B.V. All rights reserved.