Abstract: Cast iron modifier contains, in % by weight:______________________________________ silicon from 30 to 40 rare-earth elements from 2 to 8 calcium from 10 to 20 aluminum from 15 to 30 carbon from 10 to 30 sulphur from 0.1 to 0.3 iron the balance, ______________________________________The above components being added to molten cast iron in the form of a mixture of alloys and cupola coke containing, in % by weight: ______________________________________ silicocalcium from 30 to 55 silicomishmetal from 5 to 25 silumin from 15 to 30 cupola coke from 10 to 30, ______________________________________The amount of the mixture added to cast iron being from 0.4 to 0.8% by weight.The modifier enables the manufacture of thin-walled cast iron castings without formation of cementite on their surface.