Casillas was an indispensable figure in Madrid's march to the Primera Division title last season and also proved to be a rock between the posts for Spain in their Euro 2012 triumph.
Ramos, who is also Casillas's teammate in the Spain national team, believes that the 31-year-old deserves to be recognised for his achievements.
"I don't know what to say about this topic as there's no clear criteria when it comes to awarding the Ballon d'Or," he is quoted as saying on Madrid's official website.
"It would be fair to award it to a defender or goalkeeper. How can I not award it to Casillas?
"Only one goalkeeper has won it before, and I would give it to Casillas because you can always count on him as a goalkeeper and as a captain. He's the best in the world."
However, Ramos cannot ignore the feat of Cristiano Ronaldo for Madrid in 2011-12, in which he scored 46 goals in 38 league matches and also led the Spanish giants to the semi-finals of the Champions League.
"But at the same time how am I not going to give it to Cristiano Ronaldo?" he said. "There is no one like him and he makes the difference."
Madrid are currently on a pre-season tour of the USA.