Health minister Stoycho Katsarov confirmed the move on Friday (16 July), effective from Monday (19 July) citing concerns about the rising number of Covid cases in the UK.
Bulgaria also added Spain, Cyprus, Fiji and Kuwait to its red list.
It means only Bulgarian citizens, long-term residents and their immediate family will be able to enter the country from the UK.
The decision to red list the UK came just days after the UK government placed Bulgaria on its green list.
On Wednesday (14 July), transport secretary Grant Shapps confirmed that from 4am on Monday (19 July), Bulgaria and Hong Kong would be added to the UK’s green list, and Croatia and Taiwan to the green watchlist.
The Foreign Office updated its travel advice on Friday to reflect the change.
"Bulgaria has a system of classification for travellers arriving in the country based on green, orange and red zones," said the FCDO.
"From Monday 19 July, the UK will be categorised as a ‘red zone’ country. This means only Bulgarian nationals, long-term residents in Bulgaria and family members travelling from UK are allowed to enter the country."
