The state prosecutor Frederic Fevre had recommended Mr Strauss Kahn's acquittal, saying there was not enough evidence to back up the pimping charge.
The chief judge said Mr Strauss-Kahn behaved as a client and had not paid the sex workers he met. He only benefitted from others paying them to be present for group parties, the judge added.
Five of the six plaintiffs - including four prostitutes - had also dropped their accusations against the 66-year-old.
Dominique Strauss-Kahn has always denied knowing that some of the women who took part in orgies he attended were prostitutes.
Earlier Censor.NET informed that Gerard Depardieu did not appear at court were he was accused of drink driving because of his preparing the role of Dominique Strauss-Kahn.