To provide a worm gear oil composition having excellent transmission efficiency and having little adverse influence to rubbers and coatings used in oil seal and the like.

The worm gear oil composition for worm gear units consisting of a high tensile brass wheel and a steel worm comprises (A) at least one species base oil selected from (a) polyolefin-based base oils, (b) mineral oils and (c) alkyl group-substituted aromatic base oils and (B) a partial ester compound comprising a fatty acid and an aliphatic polyhydric alcohol having a 6-30C hydrocarbon group, wherein the content of the component (A) is 60-94 mass% and the content of the component (B) is 6-40 mass% based on the total weight of the composition.

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