A SYDNEY woman accused of cutting her former lover's penis in an attempt to castrate him has pleaded not guilty to murder but guilty to manslaughter.

Jian Chen was arraigned in the NSW Supreme Court today, where the crown accepted her guilty plea to the less serious offence of the manslaughter of Xian Peng, 48, in February 2011.

The matter was put over to August 10 for a sentencing hearing.

The then 48-year-old Chen was arrested last year when she appeared in Burwood Local Court.

According to a statement of facts before that court, police said she had used sleeping pills to spike the soup she gave her former partner at her North Ryde home on February 9.

Peng had only recently returned to Australia from China with a new girlfriend, the statement of facts said.

Once Mr Peng was asleep, Chen allegedly bound his hands and feet and stabbed him a number of times in the neck and groin, before cutting his penis and scrotum.

"An attempt to castrate him had taken place," said the police facts.

"The victim also had lacerations to the left side of his groin and his penis had been scalped."

Chen, who ran a business importing seafood, allegedly called an ambulance, saying she had just stabbed her boyfriend.