Cobalt boride (Co2B) is a significant transition metal boride having a wide range of usage area due to its high oxidation, abrasion and corrosion resistance as well as its superior electrochemical, magnetic and anisotropic properties. In this study, pure Co2B nanocrystals were synthesized with Co, B2O3 and Mg as starting materials via the mechanochemical synthesis (MCS) method by high-energy planetary ball mill in a hardened steel vial with hardened steel balls. All the experiments were conducted under Ar atmosphere at different rotational speeds and at 20 : 1-30 : 1-40 : 1 ball-to-powder ratios. Leaching of Co2B + MgO powder mixtures occurred after milling and purified with acetic acid and pure Co2B nanocrystals were obtained in solid form. The Co(2)Bs were characterized through X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer, Brunauer-Emmett-Teller and specific density analyses, and effects of synthesis parameters on product properties were revealed. Surface areas of the powders synthesized at 40 : 1 ball-to-powder ratio at different rotational speeds were measured as 21.14, 40.36 and 52.33 m(2) g(-1), respectively. Crystallite sizes of Co2B nanocrystals were between 7.27 and 9.84 nm and their specific density varied between 7.61 and 7.78 g cm(-3). It was determined that all samples were saturated and exhibited hysteresis and ferromagnetic behaviours, and saturation magnetization was between 35 and 50 emu g(-1).