Carbon black-phenolic resin composite binders with various amounts of nanoscale carbon black were prepared through adding KH-550 coupling agent and high-speed mixer.The effects of nanoscale carbon black amount added on viscosity of the composite binders were studied.Low-carbon MgO-C specimens were fabricated with these composite binders.Effects of nanoscale carbon black contents(0,2.5%,5%,10%,and 15% of phenolic resin in mass percent)on mechanical properties of low-carbon MgO-C specimens were investigated.The results revealed that the viscosity of the composite binder increased rapidly with increase of nanoscale carbon black content,and that CMOR,HMOR(high modulus of rupture)and CCS(cold crushing strength)of the specimens increased gradually with increase of nanoscale carbon black content as well. Carbon black-phenolic resin composite binders with various amounts of nanoscale carbon black were prepared through adding KH-550 coupling agent and high-speed mixer. The effects of nanoscale carbon black amount added on viscosity of the composite binders were studied. Low-carbon MgO -C specimens were fabricated with these composite binders. Effects of nanoscale carbon black contents (0, 2.5%, 5%, 10%, and 15% of phenolic resin in mass percent) on mechanical properties of low-carbon MgO-C specimens were investigated the results revealed that the viscosity of the composite binder increased rapidly with increase of nanoscale carbon black content, and that CMOR, HMOR (high modulus of rupture) and CCS (cold crushing strength) of the specimens increased gradually with increase of nanoscale carbon black content as well.