In this work, the structural, magnetic and mechanical properties of Nd16 Fe76-xCoxB8 alloys with a varying Co content of x = 0, 10, 20 and 25 were experimentally investigated by X-ray diffraction (XRD), Mossbauer spectrometry (MS) and vibrating sample magnetometry (VSM) at room temperature (RT), and microhardness tests were performed. The system presented hard Nd2Fe14B and the Nd1.1Fe4B4 phases for samples with x = 0; when the concentration increased to x = 20 and 25, the CoO phase appeared. All MS data showed ferromagnetic behavior (eight sextets: sites 16k1, 16k2, 8j1, 8j2, 4c, 4e, sb) associated with the hard and soft magnetic phases, and one paramagnetic component (doublet: site d) associated with the minority Nd1.1Fe4B4 phase, which was not identified by XRD. All samples were magnetically hard and presented hard magnetic behavior. The increase of Co content in these samples did not improve the hard magnetic properties but increased the critical temperature of the system and decreased the crystallite size of the hard phase. There was a general tendency towards increased microhardness with cobalt content that was attributable to cobalt doping, which reduces the lattice parameters and porosities within the sample, improving its hardness.