A cathode block for aluminum refining containing a calcined coke in a proportion of 15 to 100 wt %, characterized in that the calcined coke is prepared by mixing a heavy oil having a content of quinoline insoluble components of 10 to 25 wt % with 3 to 20 wt % of carbon black, and subjecting the resultant mixture to coking and then calcination. The cathode block for aluminum refining is excellent in resistance to abrasion and thus has a prolonged life.