Three assailants pounced on the taxi as it got stuck in traffic in the northern suburb of Saint-Denis on Friday morning, said a police source.
They broke the window of the back seat, and snatched Swank's designer bag from her hands.
Motorists often fall victim to smash-and-grab robberies in this part of town, which has regular traffic jams.
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Swank, 38, has been awarded two Oscars -- for her role in the 1999 film "Boys Don't Cry" and for 2004's "Million Dollar Baby".