China's official foreign currency reserves fell in the last three months of 2011.
Figures issued on Friday showed that reserves held by the People's Bank of China slipped 0.6% to $US3.18 trillion. The BBC reports it was the first quarterly decline since 1998.
Beijing's stock of foreign currencies is still by far the biggest in the world.
Analysts say the fall in reserves may be a sign of speculators moving their money out of the Chinese currency because they expect it to fall against the US dollar.
It also reflects China's trade surplus, which narrowed for a third consecutive year in 2011, falling to about $US160 billion compared with its record high of $US295 billion in 2008.
The Shanghai Composite Index closed down 1.3% on Friday, accelerating its losses after the reserve figures were released.