Lothian and Borders Police are appealing for witnesses after the rings were stolen from the jewellery shop on the busy thoroughfare of George Street in Edinburgh.
The incident happened at 1.10pm in the Lime Blue Diamond Store when a man described as being in his 20s walked in and asked to look at rings.
When the assistant removed the rings from the display cases, the man snatched them and ran out of the store.
Police said he may have got into a dark-green car.
Detective Sergeant Lynsey Thomson said: "I would appeal to anyone in the area who might have seen something to let us know as soon as possible."