Made in 1931, they stood outside the former Alcan factory in Southam Road, Banbury, where metal for World War II planes were manufactured.
Thames Valley Police believe they may have been sold for scrap.
Cherwell District Councillor Kieron Mallon described the theft as "a devastating blow" for the town and its industrial heritage.
Mr Mallon, himself a former Alcan employee, said: "The site and the Alcan premises are very much a local landmark.
"Sadly, it looks as though the gates presented too good an opportunity for thieves to miss out on."
Thames Valley Police are appealing to anyone who may have noticed a vehicle or suspicious activity in the area sometime before the gates were stolen on 3 October.
The Alcan factory closed in 2007 with the loss of around 300 jobs. It was demolished in 2009.
Thieves have stolen a set of Grade II listed metal gates from a former Oxfordshire factory.