The former Manchester United player surpasses his fellow footballers on the social networking website, with Brazilian Kaka the closest to him with 20.9 million followers.
Ronaldo, who has posted just over 2,100 tweets since joining the site back in June 2010, wrote: "Wow! Reached the 30 million followers on Twitter, it's amazing. Thanks everyone."
The next biggest sports star away from football who comes closest to Ronaldo is NBA player LeBron James, who has 14.8 million followers.