The Justice Ministry in China says lawyers are now required to swear allegiance to the ruling Communist Party for the first time.
All lawyers obtaining or renewing their professional licence will have to pledge their loyalty to the country and the leadership of the party.
Critics see the move as lacking legal basis and ''inappropriate''.
The oath was necessary to raise lawyers' political, professional and moral standards, said the ministry.
It has also named institutions to organise the oath-taking ceremonies and specified that lawyers need to take the pledge within three months from the date on their certificates, state media Xinhua news agency reported.
The new requirement comes at a sensitive time of political transition, with the Communist Party preparing for a once-in-a-decade leadership transfer later this year.
In recent years, the Chinese authorities have increased pressure on lawyers who take on politically sensitive cases.
Last year, authorities suspended or revoked licenses to deter lawyers from taking on cases defending government critics and human rights activists.
Some lawyers, such as the high-profile dissident Gao Zhisheng and blind activist Chen Guangcheng, were secretly detained or put under house arrest.
Mr Gao, who was arrested in February 2009, was released briefly in March 2010 and disappeared soon after. His family was told in January this year that the lawyer, known for defending religious minorities and activists, was in a jail in the remote Xinjiang area.
Mr Chen, known as the "barefoot lawyer", clashed with the authorities over the enforcement of China's one-child policy. He defended women whom he said were being forced into late-term abortions and being sterilised by over-zealous health officials in Linyi city, Shandong Province.
Several lawyers have already expressed concern at the announcement, describing it as inappropriate, baffling, without legal basis and harmful to the rule of law.
Jiang Tianyong, a lawyer for Aids activists, was detained for two months last year. He said the measure was ''ridiculous in a modern society'' and ''unimaginable in any other country''.
"As a lawyer, you should only pay attention to the law and be faithful to your client," another well-known rights lawyer, Mo Shaoping told Reuters news agency.
"The oath will hurt the development of the Chinese legal system."