A Beijing lawyer who has become a defender of the rights of "er nai", or mistresses, has lost the love from his wife.

Four months ago, Zheng Baichun set up a website offering legal advice to women in relationships with married men. Over 100 mistresses have asked for his help.

He believed mistresses are vulnerable as many are from poor families and their basic rights should be respected.

Any unmarried woman who has a stable sexual relationship with a man and receives financial support from him has legal rights that need protecting, said Zheng.

His website and his ideas have led to some harsh criticism. It is not unusual for rich and powerful Chinese men to keep one or more mistresses who often end up being the targets of criticism for corrupting public morals.

Zheng said mistresses are often afraid to resort to the law to safeguard their rights which can be undermined by society's moral standards rather than ruled by law.

Despite the controversy, Zheng's website has received more than 36,000 visits.

He has helped four women so far. In one case he helped a woman win child support from a man who fathered her son in an affair more than 13 years earlier.

Zheng insisted that his advocacy work did not mean he supported women to become mistresses.

Zheng's wife apparently didn't share the lawyer's commitment to his just cause and she has filed for divorce.

His bold move has also won some recognition. Guo Huimin with the Northwestern Polytechnic University said the legal rights of mistresses should not be denied. "Moral wrongs and legal issues should not be confused."