Two-time Grand Slam winner Li Na has announced her retirement after failing to overcome from a series of persistent knee injuries.

The 32-year-old world number six claimed victory at the Australian Open in January to add to her 2011 French Open title.

However, she had not played since losing in the third round at Wimbledon in June and underwent knee surgery in July.

"Walking away from the sport, effective immediately, is the right decision for me and my family," she said in an open letter released today.

"It took me several agonizing months to finally come to the decision that my chronic injuries will never again let me be the tennis player that I can be.

"After four knee surgeries and hundreds of shots injected into my knee weekly to alleviate swelling and pain, my body is begging me to stop the pounding.

"While I've come back from surgery in the past, this time it felt different. As hard as I tried to get back to being 100%, my body kept telling me that, at 32, I will not be able to compete at the top level ever again."

Li added that she plans to stay involved in tennis by opening her own academy in her native China.