The 34-year-old had a glittering career, helping Brazil win two World Cups and being named Fifa World Player of the Year in 1996, 1997 and 2002.
He had been expected to quit at the end of the season but the early elimination of his club, Corinthians, from the Copa Libertadores brought forward the date.
"I wanted to continue, but I can't. I think of an action, but I can't do it the way I want to. It's time," he said.
Ronaldo's career took him to some of Europe's top clubs, including Spanish rivals Barcelona and Real Madrid, as well as Italian neighbours AC Milan and Inter Milan.
But it was on the world stage where he made the biggest impact, scoring a record total of 15 goals at three World Cups.
