Metal ferrites nanocrystallites, MFe2O4 (M = Mn, Co, Ni, Zn) were prepared by coprecipitation method and characterized by a combination of physico-chemical and spectroscopic techniques. MFe2O4 nanoparticles having particle size in the range 10-35 nm were tested as catalysts in the oxidation of o-phenylenediamine (OPD) to 2,3-diaminophenazine (DAP) using hydrogen peroxide as oxidant at room temperature. Kinetic data was collected for the catalytic oxidation of OPD to DAP by monitoring the UV-vis absorbance at 415 nm and fit well to the Michaelis-Menten model yielding kinetic parameters K-m (Michaelis-Menten constant) and V-max (maximum rate of reaction). MnFe2O4 nanoparticles provide the highest catalytic activity in the oxidation of OPD to DAP at room temperature. A colorimetric method was developed based on the MnFe2O4/OPD system for the detection of H2O2 in reaction solution. The method has a detection limit of 30 mu M for H2O2 and wide linear range.