Composite nanoparticles (NPs) of FeCo-Ag and FeCo-Au fabricated by the redox-transmetalation technique are characterized by transmission electron microscopy (TEM), X-ray diffractometry (XRD), Mossbauer spectroscopy and magnetometry. TEM images prove the formation of agglomerated quasi-spherical NPs with mean value of diameter < D > about 28 run. As indicated by XRD and Mossbauer spectroscopy composite NPs constitute cores containing Fe3+ Co-based oxides with smaller contribution of bcc alpha-FeCo alloy and shells representing well crystallized Ag and Au. Mean value of diameters < 1) > of magnetic cores (approximate to 10 nm) and non-magnetic shells (approximate to 18 nm) in composite NPs are estimated by complementary analysis of TEM images, broadening of XRD reflections and approximation of hysteresis curves M(H) with Langevin function.