The Catalan regional authority is seeking to hold an independence referendum on Oct. 1 which the Spanish government says is illegal. The government says it is doing everything possible to stop it.
"Catalan independence would be absolutely irrational from an economic point of view," he said in an interview with radio station Cadena Cope, Xinhua news agency reported.
An independent Catalan republic would be outside the European Union and that would leave products open to tariffs, leading many companies to relocate, while the Catalans would also have to set up their own currency, the minister said.
"The overall impoverishment would be brutal. GDP could fall by between 25 and 30 percent and the unemployment rate would double," added the minister.
Catalonia, which receives more tourists than any part of Spain, accounts for around 20 percent of the Spanish GDP and currently has an unemployment rate of just over 13 percent, well below the Spanish average of slightly over 17 percent.