A first trial in January 2017 collapsed, despite the court finding evidence of a "clear attempt" by Wildenstein and seven codefendants to conceal the bulk of their vast fortune.
The presiding judge said lapses in the investigation and French law made it impossible to return a guilty verdict.
Prosecutors appealed but the higher court confirmed the judgement.
It found that in one case "the crime of tax fraud is outside the statute of limitations", which was three years at the time of the alleged offence, and in the other that insufficient proof and legal loopholes torpedoed the case.
Wildenstein's nephew, Alec Junior, and his ex-stepsister Liouba Stoupakova were also cleared, as well as trust fund managers and lawyers who were also on trial.
The case was based on tax declarations filed in 2002 and 2008, following the deaths of patriarch Daniel and his eldest son Alec.
Guy Wildenstein, 72, is the heir of three generations of wealthy art dealers and thoroughbred racehorse breeders and the alleged discrepancies came to light during a battle over inheritance.
Prosecutors said that most of the dynasty's billions are held by a web of trusts and holding companies stretching from the Channel Island of Guernsey to the Bahamas.
In another case French tax officials are claiming more than half a billion euros from the family.