The citrate precursor method has been used to synthesise ultrafine NiFe2O4. The citrate precursor, Ni3Fe6O4(C6H6O7)(8) . 6H(2)O, was isolated by thermal heat treatment at around 100 degrees C. Thermal decomposition of the hydrated precursor was investigated by TG, DTA and DTG techniques, and gas and chemical analyases. The citrate precursor, on decomposition in air, yields pure and stoichiometric NiFe2O4. The decomposition consists of three major steps. The dehydration step of the citrate precursor is overlapped by the formation of an acetonedicarboxylate complex. The citrate groups are completely destroyed in the temperature range 200-320 degrees C resulting in the formation of NiFe2O4 with the evolution of acetone and CO2 gas. The free CO2 gas is trapped in the lattice and is released above 320 degrees C. The ultrafine NiFe2O4 particles have been observed as clusters having a crystallite size of 5.93 nm and a surface area of 120.0 m(2) g(-1). The citrate precursor and decomposed products were characterized by IR, NMR, XRD, SEM and surface area measurements.