The twin brothers were born prematurely in Xi'an, provincial capital of Shaanxi. The elder boy weighed about two kilogrammes at birth.
When doctors checked a mass in his abdominal area, they discovered to their surprise that it looked like afetuswith bones and nails, state-run China.Org reported.
What happened to the baby is known as foetus in foetu, an incredibly rare occurrence which affects only one in every 500,000 births, the report said.
The third foetus was taken out 15 days after the boy was born. The cause of the condition remains unknown, the report said.