ABSTRACTNanomagnetic fluid a novel material comprising of ferromagnetic nanoparticles has been evaluated as a corrosion inhibitor. Corrosion behavior of carbon steel in 5% HCl has been studied as a function of various concentrations of aqueous nanomagnetic fluid. The novel nanomagnetic fluid has been specially synthesized to achieve the stability in acidic media when it is mixed with 5% HCl This nanomagnetic fluid has been evaluated by gravimetric and polarization measurement techniques. It was observed that the inhibition efficiency increases with the increase in the nanomagnetic fluid concentration and reaches the maximum at the optimum concentration. This is further confirmed by the decrease in the corrosion rate. It is found that the system follows a Temkin adsorption isotherm. Keywords: nanomagnetic fluid acid corrosion polarization.