William Gray, 64, of North Wildwood, N.J., pleaded guilty to theft of government property and income tax evasion, WCAU-TV, Philadelphia, reported Friday.
In federal court, Gray admitted to taking $1 presidential coins, all missing lettering on their edges, and selling them to a California coin dealer knowing they were more valuable to collectors because they were "mint errors."
Gray also admitted he did not pay taxes on the money he got for the coins, The Philadelphia Inquirer reported.
Gray, who worked at the mint from 1996 until January, is free on $50,000 bail pending a sentencing hearing set for Dec. 20.
Jordana Brewster on Paul Walker: 'He was an enormous presence in my life'
Gal Gadot cast as Wonder Woman for 'Batman vs. Superman'