Alfonso Dastis claimed his government would ensure that the lives of ordinary Britons in the country are "not disrupted" in the event of a "no deal" Brexit.
Spain is host to the largest number of British citizens living in the EU (308,805) and just over a third (101,045) are aged 65 and over, according to the Office for National Statistics.
Theresa May is facing pressure from some Tories to leave the EU without an agreement so Britain can free itself from Brussels regulations, avoid a costly "divorce bill" and take what some see as full advantage of the benefits of Brexit.
The minister told BBC One's Andrew Marr Show: "I do hope that there will be a deal.
"If there is no deal we will make sure that the lives of ordinary people who are in Spain, the UK people, is not disrupted.
"As you know, the relationship between the UK and Spain is a very close one in terms of economic relations and also social exchanges.
"Over 17 million Brits come to Spain every year and many of them live here or retire here and we want to keep it that way as much as possible."
The pledge came as International Trade Secretary Liam Fox said a commercial relationship with the bloc would only fail if the EU “punished Britain for having the audacity to leave”.
He warned Brussels to put the prosperity of EU citizens ahead of any desire to make the UK pay a price for quitting the bloc, and sign a mutually beneficial trade agreement.
Shadow foreign secretary Emily Thornberry warned that "intransigence" from Theresa May has left Britain "heading for no deal".
Thousands of anti-Brexit activists march to Parliament in protest
And Dr Fox said leaving without an agreement and trading on World Trade Organisation (WTO) terms was "not exactly a nightmare scenario".
But he stressed he would "prefer to have a deal because it would give greater certainty and almost certainly greater openness" and said reaching agreement does not need to be complicated if there is political will.
"I don't think they're (the negotiations) difficult in terms of the trade law or the trade negotiations themselves. The difficulty is the politics," Dr Fox told ITV's Peston On Sunday.
"In other words, how much does the European Commission and the European elite want to punish Britain for having the audacity to use our legal rights to leave the European Union.
"That's the thing.
"And what will the price be for the prosperity of European citizens of that decision?
"I would hope that economic sense would dictate that we put the prosperity agenda of the whole of the European continent in a global context at the top of that agenda not ever closer union, in other words the drive by the Commission towards their political objective which has a near-theological level."
The Prime Minister is continuing to negotiate so-called withdrawal issues with the EU, including expats' rights, a financial settlement and the Irish border.
Only when "sufficient progress" is made in these areas will Brussels chief negotiator Michel Barnier recommend that EU leaders give the green light to talks on a future trading relationship.