The field dependence of the magnetization at 4.2 and 294 K and the temperature dependence of the spontaneous magnetization for two series of ternary Co‐based alloys, namely Co76−xB24Cxand Co88−yByC12have been measured. The metalloid content in these series ranges from 24 to 44 at.%, and extends almost to the critical concentration for the disappearance of ferromagnetism. The composition dependence of the average magnetic moment at 4.2 K compares well, for low metalloid content, with data for other Co‐based materials and also with the theoretical models that predict a linear dependence of the magnetic moment as a function of concentration. The thermal demagnetizing process at low temperatures is presented. The results have been analyzed in terms of Bloch’s law and the stiffness constant has been determined. The complete thermal demagnetization, i.e., down toTc, is presented only for the alloys with a Curie temperature below 300 K. The results show the well known flattening of theM(T) curve as compared with crystalline materials.