They released photographs of items seized in the raids, including a pile of human teeth, pills and numerous unsterilized forceps and dental tools.
Police said they detained eight Chinese suspects in a year-long operation and shut down six "clandestine medical clinics" in the Usera district of southern Madrid, which is home to a large Chinese community.
As well as those held in custody, police brought charges against two others for crimes against public health and unlicensed professional activity.
"They offered gynaecological, paediatric and dental consultations among other specialities, and even carried out surgical operations and abortions in private homes lacking the required hygiene and security conditions," a police statement said.
Photo: Spanish National Police
It noted "the deplorable state of the premises and medical equipment used" and said a number of the patients treated were young children.
The unlicensed "doctors" advertised their services in media targeted at the Chinese community.
The racket was exposed after a patient reported to police one of the bogus doctors who charged him €3,500 euros for a series of visits for stomach pains.
The doctor faked the man's blood-test results to make him think he had hepatitis and gave him pills. The pains worsened and he ended up being treated in hospital for a stomach infection.