We report the microwave-hydrothermal ionic liquid (MHIL) synthesis and photocatalytic property over phenol of ZnFe2O4 nanoparticles. Zn(CH3COO)(2)center dot 2H(2)O and Fe(NO3)(3)center dot 9H(2)O were used as the zinc and iron sources, respectively, in the presence of CO(NH2)(2) and the ionic liquid 1-n-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM][BF4]). Deionized water was used as a solvent. The ionic liquid [BMIM][BF4] and microwave heating temperature have significant influences on the crystal phase of the product. Different dosages of [BMIM][BF4] or microwave heating temperature could lead to the formation of different products such as ZnFe2O4 and beta-FeOOH. The MHIL method has the advantages such as simplicity, rapidness and energy saving. The ZnFe2O4 nanoparticles prepared by the MHIL method exhibit high photocatalytic activity for the degradation of phenol, which was up to 73% within 360 min. The TOC measurement confirmed the good photocatalytic efficiency of ZnFe2O4 nanciparticles. (C) 2009 Elsevier B.V. All rights reserved.