In a statement it said that Carlo Alberto Capella was ordered to face trail on Thursday, with the first hearing set for June 22.
Capella, who was in office until last year, was recalled from Washington by the Vatican in September.
The US State Department notified the Vatican in August through diplomatic channels of a possible violation of child pornography laws by a member of its diplomatic corps in Washington, the Vatican said at the time.
It is the latest case the Catholic Church has faced after repeated criticism for the way it has handled scandals over paedophile priests.
In May the pontiff promised to "restore justice" after reading the conclusions of an investigation into the abuse, carried out after his defence of Chilean bishop Juan Barros -- accused of covering up Karadima's abuses -- caused a public outcry.
He later apologised to three of Karadima's victims at the Vatican and last weekend he received seven more people abused by the priest, who was suspended for life by the Vatican.
Two weeks previously 34 Chilean bishops announced their resignation over the scandal after being summoned to the Vatican by Francis.
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