The influence of magnetic field on effective interfacial area in a slurry bubble column of magnetizable particles (magnetic) has been studied by using the theory of absorption accompanied by chemical reaction. The model system used was oxidation of sodium sulphite in presence of cobalt sulphate as catalyst. The effective interfacial area increases with the increase in intensity of magnetic field. The increase was approximately 1.4 times (a(H)/a(H=0)=1.4) for a field strength of 462 Oersteds with 2% magnetite concentration.