In this work, magnetic sensitive hydrogel (ferrogel) was prepared by gamma irradiation of poly(ethylene glycol) (PEG)/ methacrylic acid (MAc) blends in the presence of Fe3O4 particles. The release of vitamin B12 from ferrogels was studied in the absence of magnetic field (MFOFF) and under switching magnetic field (MFON). Different parameters such as effect of MAc ratio, temperature, pH and magnetic field on swelling and the release characters of vitamin B12 were investigated. The PEG/MAc ferrogels displayed magnetic sensitivity, in which the release of vitamin B12 increased greatly under switching magnetic field. The permeability coefficient (P) was calculated. The results suggested that this type of ferrogels may be considered as magnetic sensitive drug delivery systems.