Denis Lyons, 78, pleaded guilty Friday to four felony counts of lewd acts upon a child under 14, the Los Angeles Times reported.
Lyons said he assaulted the boy four times at St. John the Baptist Catholic Church in Costa Mesa between Jan. 1, 1992, and Dec. 1, 1995. The boy was between the ages of 7 and 9.
The victim, now 26, came forward in 2008.
Prosecutors expected Lyons to be sentenced May 25 to one year in jail and five years' probation. He will also be required to register as a sex offender for life.
In 2003, Lyons was charged with molesting three boys between 1978 and 1981, also at St. John's. At that time, the U.S. Supreme Court struck down a California law that allowed prosecution of older sexual abuse cases, which prevented prosecutors from pursuing charges for crimes that occurred before 1988.
A spokesman for the Roman Catholic Diocese of Orange County said last week Lyons was removed from ministry in 2002 and "was committed to a life of prayer and penance."