A bike locked up outside a shop in Northampton had gone when the owner came back.
The white and grey Ammaco CS650 mountain bike was locked up outside a shop at the Riverside Retail Park.
When the owner returned a short time later, both the bike and the lock had been taken.
The theft happened at about 3.35pm on Saturday, February 21.
Witnesses, or anyone with information, can call Northamptonshire Police on 101.
Alternatively, they can call the independent charity Crimestoppers anonymously on 0800 555 111 or use the anonymous online form at www.crimestoppers-uk.org.