Abstract: Cr—Mo alloy steel suitable for motor vehicle transmission gears and shafts is provided and can avoid solve problems associated with. Preferred Cr—Mo alloy steel of the invention comprises steel as a major component, about 0.17 to about 0.21 weight % of carbon, about 0.15 weight % or less of silicon, about 0.60 to about 0.85 weight % of manganese, about 0.02 weight % or less of phosphorus, about 0.03 weight % or less of sulfur, about 1.25 to about 1.45 weight % of chrome, about 0.55 to about 0.65 weight % of molybdenum, and about 0.015 to about 0.035 weight % of niobium.