Spain is the latest country to become embroiled in a spying row with Russia.
Two Russian diplomats were expelled from Madrid in November for what Spain calls "activities incompatible with their status".
Russia responded by expelling two Spanish diplomats last week.
The Spanish foreign ministry said the two Russians were expelled "for activities incompatible with their status as diplomats" - the diplomatic term for spying.
It said both governments considered the incident "resolved".
The BBC reports the ministry would not comment on reports the Russians had engaged in economic espionage.
The newspaper El Pais said it is the most serious diplomatic incident between the two countries since Moscow restored diplomatic relations with Madrid in 1977.
Earlier in December, Britain expelled a Russian diplomat and Russia responded in kind.