Magnetic-field-sensitive gel, called ferrogel, was prepared by a two-step procedure in which first step requires synthesis of the poly(N-tert-butylacrylamide-co-acrylamide) [P(NTBA-co-AAm)] hydrogel and during second step magnetite (Fe3O4) particles were formed in the hydrogel via coprecipitation of Fe(II) and Fe(III) ions in alkaline medium at 70 degrees C. The obtained ferrogel was characterized by attenuated total reflectance Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy combined with energy dispersive spectroscopy, and electron spin resonance measurements. The magnetic responsive of the ferrogel was also investigated by applying magnetic field to the ferrogel. The extent of a bending degree of the ferrogel depends on the applied magnetic field strength. In addition, the magnetic responsive studies also indicated that formed magnetite content in the hydrogel is high enough to achieve considerable magnetic response to external magnetic field. As a result, the P(NTBA-co-AAm) ferrogel may be useful for potential applications in magnetically controlled drug release systems, magnetic-sensitive sensors, and pseudomuscular actuators. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 800-804, 2009