US District Judge John E Sprizzo on Monday called the actions of the apartheid regime "repugnant" and said decisions by the corporations to do business with the regime may have been "morally suspect or embarrassing".
But he said there was no meaningful assertion by the plaintiffs that actions by US corporations directly caused the alleged murders, torture, crimes against humanity and other heinous acts in South Africa from 1948 until a decade ago.
The ruling stemmed from lawsuits filed in federal courts against defendants that included some of the nation's largest corporations.
The lawsuit had alleged that the apartheid regime tracked African individuals on US-made computers, obtained loans from US banks and kept its military machines in working order with US-supplied oil.
SA government didn't support lawsuits
In tossing out the suits, Sprizzo said they bordered on the frivolous and noted that it was his job to "apply the law and not some normative or moral ideal".
He said the defendants had made no claims that the US corporations participated in torture, genocide, killings and other serious crimes.
"At most, by engaging in business with the South African regime, defendants benefited from the unlawful state action of the apartheid government," he said.
The judge said the current South African government had indicated it did not support the lawsuits and that letting them proceed might injure the government's ability to handle domestic matters and discourage investment in its economy.
A message left with a lawyer for the plaintiffs was not immediately returned.
Owen C Pell, a lawyer for defendant Citigroup Inc, said the judge ruled correctly because he followed the guidance offered by the Supreme Court in its most recent rulings related to the subject."