The theft occurred sometime between the afternoon of March 21 and 7.30am on March 22.
Thames Valley Police said the offenders smashed the street-facing window of the shop in Turl Street and stole a large amount of jewellery including rings and brooches.
Traces of blood were left at the scene, indicating that the burglars probably injured themselves.
Some of the jewellery was later found on towpaths off Dale Close, known locally as Gasworks Bridge, and so the offenders are believed to have taken that route.
Investigating officer Det Con Rob Prout, of Force CID based at St Aldates police station in Oxfordshire, said: “I am asking anybody who did witness anything to make contact with police.
“I would also ask anybody who was driving in the area and has dash-cam, to please check this and make contact with us if it has picked up anything that may be able to assist in this investigation.”
At this stage no photos of the stolen jewellery are available.
Anyone with information should call 101 quoting reference 43200094657 or call the independent charity Crimestoppers on 0800 555 111.