Spain received 19 million international tourists last year, national statistics office INE said, down from 83.5 million in 2019 when it was the world's second-most visited country after France.
The last time Spain had so few foreign tourists was in the late 1960s.
France overtook Britain as Spain's most important source of tourists last year, accounting for 3.9 million arrivals, a 65 percent decline over 2019.
The number of British visitors was down 82.4 percent to 3.2 million, making Britain Spain's second biggest source of visitors in 2020 followed by Germany.
Britain in July imposed a mandatory 14-day quarantine on travellers from Spain, prompting many Brits to cancel their reservations at Spanish resorts during the peak summer season.
Britain has been Spain's most important source of tourists in the decades since the country began to open up to northern European holidaymakers and a sun and sea destination in the 1960s under former dictator Francisco Franco.
The plunge in arrivals has hammered Spain's tourism-dependent economy, which contracted sharply by 11 percent in 2020 in one of the worst results of the eurozone
Around 14 percent of Spanish hotel jobs, or 190,000 posts, were cut in 2020, according to Spanish union CCOO.