The former chief of embattled oil company Yukos, currently serving an eight-year sentence for fraud and tax evasion in a Siberian colony, received the reprimand last December for leaving his workplace in the colony's clothing factory without asking his supervisors for permission, Larissa Zhukova said.
Khodorkovsky's lawyers proved to the court that their client had been looking for a mechanic to get his sewing machine fixed.
Fellow inmates interrogated as part of an inquiry said they would also have left the premises without asking for permission, but unlike Khodorkovsky faced no consequences, a defense lawyer said.
It was the second time the district court had overturned the reprimand. The first ruling was overruled in February by a regional court, which sent the case back for a retrial, citing a procedural violation.
Since receiving the reprimand six months ago, Khodorovsky has been disciplined by prison authorities twice - once for alleged possession of banned documents and once for eating in an unauthorized place. His defense team has obtained a court ruling that in at least one case the disciplinary action - which saw Khodorkovsky put in an isolation cell - was inappropriate.