The main religion of Spain is Catholicism.Well, the main religion in Spain is Catholicism. 94% of the population is Catholic, but they do have other religions there too.
Spain is 94% Roman Catholic. All the other religions only total 6%.    
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Muslims, Christians (who were all Catholics at this point) and Jews, in order of population numbers.
Hindu, Islam, and i think Jainism
christianity (catholics ), judaism and islam
Madrid, Barcelona, Valencia
Spain.
70% of Spain is Roman Catholic, 2% other religions,25% no religion. Roman Catholocism is a denomination of Christianity
There are 3 major religions in Jerusalem : Judaism, Christianity, and Islam.
Just like every major city you'll find all religions represented however Spain (and Barcelona) are very Roman Catholic and this is the main faith practised in Barcelona.