A court has heard that a Sydney woman, whose partner died after she tried to cut off his penis, was a kind and gentle person.

Jian Chen pleaded guilty to the manslaughter of her former boyfriend Xian Peng in 2011.

She drugged his soup with sleeping pills, then stabbed him and tried to cut off his penis in her North Ryde home after he returned from overseas with a new girlfriend.

Chen's ex-husband has told her sentencing hearing in the New South Wales Supreme Court the attack was out of character and she was usually gentle, kind and polite.

She is yet to be sentenced.