The church said it issued the new guidelines to help church leaders weed out candidates with "psychopathic disturbances."
Sex abuse scandals by pedophile priests have rocked the church in recent years, triggering lawsuits that have cost hundreds of millions of dollars in settlements.
"(The guidelines) became ever more urgent because of the sexual scandals," Monsignor Jean-Louis Brugues told reporters.
He stressed, however, that psychological testing was used in some seminaries as far back as the 1960s - or at least a decade before the pedophile scandals exploded in public.
"In all too many cases, psychological defects, sometimes of a pathological kind, reveal themselves only after ordination to the priesthood," the guidelines said.
"Detecting defects earlier would help avoid many tragic experiences."
The guidelines said problems like "confused or not yet well-defined" sexual identities need to be addressed.
A 2005 Vatican document said men with "deep-seated" homosexual tendencies shouldn't be ordained, but that those with a "transitory problem" could become priests if they had overcome them for three years.
The Vatican considers homosexual activity sinful.
The new guidelines reflect the earlier teaching, stressing that if a future priest shows "deep-seated homosexual tendencies," his seminary training "would have to be interrupted."
The guideline say priests must have a "positive and stable sense of one's masculine identity" and the capacity to "integrate his sexuality in accordance" with the obligation of celibacy.
The church is struggling to provide enough priests for parishes in many parts of the West because of waning vocations.
But Pope Benedict XVI has said it is more important to have good priests than a greater number of priests.
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