Catalonia, whose capital Barcelona is one of Europe's most visited cities welcomed 1.49 million foreign visitors last month, a 4.7 percent decline compared with the same time last year, figures released by national statistics institute INE showed.
The northeastern region held a banned independence referendum on October 1st which was marred by violence and followed by massive street demonstrations.
Just before the referendum several countries, including Germany, France and the United States, warned their citizens to be careful if they travelled to Catalonia and airlines allowed passengers on flights to Barcelona to change their tickets.
By comparison Catalonia, whose Costa Brava beaches help make it the Spanish region that most attracts foreign visitors, had posted a 2.7 percent rise in visitor numbers in October 2016.
All other major holiday destinations in Spain saw a jump in arrivals in October which helped visitor numbers to the entire country rise by 1.8 percent to 7.3 million over the same month last year.
Catalonia was rocked in August by a jihadist attack in Barcelona and a nearby seaside resort that left 16 dead but visitor numbers to the region still rose that month by 2.3 percent, and were up by 4.0 percent in Spain overall.
The number of foreign visitors to Spain hit a new record in 2016 -- 75.6 million -- for a fourth consecutive year, helped by security concerns in some other Mediterranean holiday destinations such as Turkey and Tunisia.
Still Catalonia remained Spain's most visited region in October, accounting for 20.5 percent of all foreign arrivals, followed by the Canary Islands and the Balearic Islands.
Last year 18 million foreigners visited Catalonia, about a quarter of the total number of arrivals to Spain, the world's third most visited country after France and the United States.