The contract, announced earlier this week, includes support and development of OneSteel plants in Newcastle in the New South Wales, Australia and Whyalla, South Australia.
The contract has an option for a further two years.
Michael Dines, OneSteel eCommerce and IT general manager said, OneSteel had "embarked on a detailed evaluation of possible outsourcing partners and CSC presented the best overall option for those services being renewed."
Mike Shove, CSC Australia managing director said OneSteel has outsourced IT services to CSC since the merger of BHP and Billiton in March, 2001. OneSteel was previously a division of BHP.