The 51-year-old actress sold the five-carat emerald-cut diamond to a Beverly Hills high-end jeweller in order to get rid of any reminders of their romance, reported Radar online.
"Ashton broke her heart. Anything that reminds her of him makes her sad, and she wants to be happy," a source said.
The former couple got married on September 24, 2005 and split in November 2011 amid claims that the 'No Strings Attached' star enjoyed a fling with student Sara Leal, 23, in San Diego on his sixth wedding anniversary.
Kutcher, 35, has since been dating his former 'That 70s Show' co-star Mila Kunis, 30.
Moore was earlier married to Freddy Moore and Bruce Willis.