Carbon can be used as a reducing agent in mechano-chemical reactions in mechanical milling. Some carbon sources have stronger reducing power in comparison to others. In this research mixtures of barium ferrite with different carbon sources (carbon black, graphite and carbon nanofiber) were milled in a high energy mechanical milling machine. The effect of carbon source reducing characteristics on the barium ferrite partial reduction was studied. Phase analysis, particles morphology and magnetic properties were investigated via XRD, HRTEM, and VSM, respectively. Phase analysis showed that the partial reduction of BaO.6(Fe2O3) via carbon black progressed to Fe1-xO stage in molar ratio of C:O = 1.1 in the milling mixture. Carbon black had the best reducing power and then graphite was better reducing agent compared to carbon nanofiber. The 40 h milled sample with carbon black reached the highest saturation magnetization of 174.65 emu/g after vacuum heat treatment at 900 degrees C. HRTEM images showed that nanocrystals of Fe3O4 forms after 40 h milling of barium ferrite with graphite.