Some 23 hedge funds, including Viking Global Investors, Glenhill Capital and Greenhill, had been seeking a total €1.36 billion in damages.
The lawsuit was one of several filed by investors against Porsche in connection with its attempted takeover of Volkswagen.
Porsche stunned markets by announcing in October 2008 that it was acquiring 75 percent of Volkswagen.
The news led to a massive surge in the value of VW shares to above €1,000.
Porsche's bid to take over VW ultimately failed and the indebted luxury car maker was in turn saved by Volkswagen, Europe's biggest carmaker.
In their lawsuit, the investment funds argued Porsche was guilty of stock market manipulation as its announcement it was taking over Volkswagen and the reasons for its move had come late.
But the regional court in Stuttgart rejected the plaintiffs' arguments. The parties can appeal the decision.
A Porsche spokesman said the ruling strengthens the company's view that claims in two similar lawsuits filed to courts in Brunswick and Hanover are also unfounded.