KFC and Bodrum Kebab, both on the Cowley Road, were serving food after the 10pm curfew.
Oxford City Council has fined two fast food takeaways for breaking coronavirus law.
Although takeaways can continue operating after 10pm using a delivery service, click-and-collect or drive-thru, the law forbids them from taking orders and serving food in their premises or at their door after 10pm.
The aim is to stop fast food takeaways forming crowds outside their premises after pubs and bars close at 10pm.
City Council officers visited both KFC and Bodrum Kebab following complaints from members of the public.
They witnessed staff at both sites serving customers and taking orders at the door on more than one occasion - and issued both with the £1,000 fine.
The City Council has the power to fine businesses up to £10,000 for breaking the coronavirus laws, but chose to issue a smaller fine as this was a first offence for both businesses.
The enforcement officers are part of the new Covid Secure Team formed last month within Oxford and countywide, to help businesses comply with the new rules and give the public peace of mind when out and about.
Alongside providing information and support, the Oxford team also carries out night-time patrols of the city centre, Cowley Road and other hotspots to provide advice and ensure businesses are following the rules.
KFC Cowley Road and Bodrum Kebab are the first fines issued by the Covid Secure Team.
Residents can report issues and concerns by email to the Covid Secure Team.
Councillor Louise Upton, Cabinet Member for a Safer, Healthy Oxford, said: “Our Covid Secure Team has been out and about across Oxford for several weeks and the vast majority of businesses are complying with the new rules.
“We’ve been particularly impressed with the pubs and bars in the city centre, many of which have gone above and beyond to ensure the safety of their staff and customers.
“But any businesses that break the coronavirus rules are irresponsibly making the city less safe for everyone, and they should know that we will take action against them.
“I would like to thank the members of the public who reported KFC Cowley Road and Bodrum to us, and encourage anyone who has concerns about a business in Oxford not complying with coronavirus rules to contact us.”