The thief gained access to the property, on Halloon Avenue, St Columb Road, at some time between 5.30pm and 9.30pm on Monday, November 26.
The key to the safe was taken off the wall and a huge amount of jewellery was taken.
Newquay inspector Dave Meredith said the crime was particularly "nasty" considering the age of the victim.
The stolen items included: three gold signet rings; a gold ladies' wedding band; a gold ring with an engraved pattern on the top; a real pearl necklace; a gold broach with a single pink stone in the middle; a gold fancy hoop chain; a gold chain and pendant with a ruby in the middle; and a gold heart-shaped locket containing photos.
Mr Meredith added: "The items have great sentimental value, in particular the heart shaped locket."
Call police on 101 with information, quoting crime reference GC/12/476.