A devout evangelical Christian, Kaká became engrossed in religion at twelve: "I learnt that it is faith that decides whether something will happen or not." He removed his jersey to reveal an "I Belong to Jesus" T-shirt and openly engaged in prayer moments after the final whistle of Brazil's 2002 World Cup, and Milan's 2004 Scudetto and 2007 Champions League triumphs. He also had the same phrase, along with "God Is Faithful," stitched onto the tongues of his boots.^[36] During the postmatch celebration following Brazil's 4–1 win over Argentina in the 2005 FIFA Confederations Cup final, he and several of his teammates wore T-shirts that read "Jesus Loves You" in various languages.

Kaká is a member of the organization Atletas de Cristo ("Athletes of Christ").^[37] His goal celebration consists of him pointing to the sky as a gesture of thanks to God. Kaká's favourite music is gospel,^[38] and his favourite book is the Bible.^[39]