The gang is thought to have smuggled some 6,000 Ukrainians into the UK and Ireland using false passports, said a statement from Spain's National Police published on Friday
Officers had arrested 56 Ukrainians with false identity documents at more than a dozen Spanish airports as they attempted to reach the UK.
Police in France, Belgium, Ukraine and Poland also arrested some 50 people, including several alleged gang leaders.
Spanish police arrested one leader in March in Barcelona and seized more than 100 ID cards and Polish passports, they said.
His arrest and the witness statements from Ukrainians detained for using false papers helped track down others in the gang.
European Union police agency Europol, which helped coordinate the operations, says migrants were offered complete packages, including ID documents, plane tickets and accommodation.
They entered Poland first and then traveled on to other countries, including transiting through airports in Spain, Belgium and France before arriving at their final destinations in Dublin and the UK.