A nine-member jury in the northwestern region of Galicia on October 30th unanimously found the pair guilty of killing their daughter, Asunta Yong Fang Basterra Porto, after one of the most closely followed criminal trials in Spain in recent years.
The girl's body was found on a forest trail near the northwestern city of Santiago de Compostela in September 2013.
Her parents had reported her missing a few hours before she was found, but the jury agreed with prosecutors that the pair had in fact conspired to kill their daughter and try to make it look like a random act of violence.
A court in Santiago de Compostela on Thursday sentenced Rosario Porto, a 46-year-old former lawyer, and her ex-husband, journalist Alfonso Basterra, 51, each to 18 years in jail for the murder, the court said in a statement.
Prosecutors charged that the murder had been planned by both parents, but carried out by the mother.
At the time of the girl's death, the couple were separated but were raising their adopted daughter together.
Prosecutors accused the parents of giving Asunta varying doses of the sedative Orfidal for several months to test its impact on her before finally giving a strong enough dose to knock her out so they could choke her to death with a rope without the girl being able to fight back.
During the trial Asunta's violin teacher told the court that two months before the girl was found dead the girl had been woozy and incapable of playing her instrument.
The prosecutors said that after strangling Asunta her mother dumped the body, which was found with a length of rope identical to rope found at a country house she owns.
The pair deny killing their daughter and have said through their lawyers that they will appeal their convictions.
The case shocked Spain and drew international attention when it came to light, prompting a statement of concern from the Chinese foreign ministry.
Asunta was adopted by the couple in China when she was less than a year old.
She was the first Chinese baby to be adopted in Galicia and her arrival in the region was covered by a local television station in which the couple spoke of their joy in finally having her in Spain after a long and complicated process.