The court has ordered Microsoft to pay a record fine of 497 billion euros ($613 million) for abusing its dominant market position and stifling innovation and consumer choice.
"The Court has upheld a landmark Commission decision to give consumers more choice in software markets," EU Competition Commissioner Neelie Kroes said.
In March 2004 the European Commission accused the software giant of violating EU competition law by refusing to give rival makers of office servers information to enable their products to work smoothly with Windows, used by 95 percent of computers. It also ordered the company to make available versions of Windows without Microsoft's Media Player.
Microsoft filed an appeal against the court's initial decision in June 2004.
Last year, Microsoft was told to pay daily fines adding up to 280.5 million euros ($389 million) over a six-month period, after it failed to comply with the 2004 decision.
In the event of the software giant contesting the latest ruling, the case could be considered in the European Court of Justice.
Microsoft has two months to appeal.
