An anti-bonding agent for blast furnace slag or its grading adjusted slag which includes one or more polymers having a main constituent unit shown by ##STR1##

by a greater molar percentage than any other constituent unit where M is hydrogen atom, alkali metal such as sodium, alkali earth metal, ammonium or organic amine is used in an amount of 0.002-0.3 weight parts for 100 weight parts of such blast furnace slag or its grading adjusted slag, and may be applied as an aqueous solution with concentration of 1.5-10 weight %.