The present study describes the synthesis of ZnMn 2 O 4 nanoparticles with the spinel structure. These oxide nanoparticles are obtained from the decomposition of metal oxalate precursors synthesized by (a) the reverse micellar and (b) the coprecipitation methods. Our studies reveal that the shape, size and morphology of precursors and oxides vary significantly with the method of synthesis. The oxalate precursors prepared from the reverse micellar synthesis method were in the form of rods (micron size), whereas the coprecipitation method led to spherical nanoparticles of size, 40-50 nm. Decomposition of oxalate precursors at low temperature (~ 450°C) yielded phase pure ZnMn 2 O 4 nanoparticles. The size of the nanoparticles of ZnMn 2 O 4 obtained from reverse micellar method is relatively much smaller (20-30 nm) as compared to those made by the co-precipitation (40-50 nm) method. Magnetic studies of nanocrystalline ZnMn 2 O 4 confirm antiferromagnetic ordering in the broad range of ~ 150 K. The photocatalytic activity of ZnMn 2 O 4 nanoparticles was evaluated using photo-oxidation of methyl orange dye under UV illumination and compared with nanocrystalline TiO 2 .