Colloidal Ni and Co nanoparticles were synthesised by a modified polyol method using sodium borohydride as a reducing agent. The influence of a gas atmosphere and a reduction temperature on nanoparticles formation was studied. A series of Co and Ni nanoparticles with the average particle sizes 1.8 to 2.8 and 2.6 to 9.8 nm, respectively, were obtained by varying synthesis conditions. Nanoparticle size was found to increase with the increase of the reduction temperature. The oxidative atmosphere was shown to favour nanoparticles growth as was demonstrated in the case of nickel.