The changes come amid increased concern over the newly discovered Omicron variant of Covid-19.
Prior to Wednesday (1 December), travellers from the UK were able to enter Spain with a vaccination certificate or a negative Covid-19 test.
The changes will mean that from Wednesday (1 December), all travellers from the UK will need to show proof of being fully vaccinated, with both doses of a two-dose vaccine or one dose of a one-dose vaccine, at least 14 days prior to arrival.