Magnetic properties of perspective nanocomposite materials based on copolymers of 1-vinyl-1,2,4-triazole with acrylonitrile and the formation of zero-valence metallic magnetic nanoparticles were investigated by electron paramagnetic resonance (EPR). In the EPR spectra of the nanocomposites intensive narrow singlets of conducting electrons with g = 2.00 were observed. The shape and width of the signals for silver and copper particles of the nanocomposites depended on microwave power. The Curie law character of the temperature dependences of intensity, g-factor value, and width of silver and copper nanoparticles' signals were determined. Paramagnetic properties of the nanocomposites were found to remain constant over a long amount of time. X-ray diffraction (XRD), scanning electron microscope (SEM), teraohmmeter measurements, and atomic absorption analysis were also used to characterize these nanocomposites. The formation of the silver and copper nanoparticles from the rise of small clusters and their growth up to stabilization within the matrix under thermoreduction of initial complexes was monitored by EPR.