The sites were found during a 250-mile patrol by law enforcement agencies involved in the protection of underwater cultural relics, China's state-run Xinhua News Agency reported.
A total of 260 diving operations lasting 220 hours were conducted during the patrol, officials said.
Archaeologists examining 12 known cultural relic sites and 12 new sites collected relics including ancient pottery and porcelain wares, copper coins and boat parts, Li Jilong of the cultural heritage bureau of Hainan province said.
The Xisha Islands are a group of about 40 islets, sandbanks and reefs, and researchers said in ancient times many Chinese merchant ships struck the reefs and sank while on their way to Southeast Asia, India and the Middle East.
Treasures and cultural relics from the wrecks are abundant in the area, archaeologists said.
Illegal salvaging of underwater cultural relics in the South China Sea has been rampant, researchers said, and traces left by thieves in some relic sites show large-scale thefts have occurred this year.