New York's main contract, West Texas Intermediate crude for delivery in May, dropped 23 cents to $103.41 a barrel.
Brent North Sea crude for May lost 47 cents to $121.24 in morning trade.
China's National Bureau of Statistics (NBS) said the world's second biggest economy expanded 8.1 percent in the first three months of 2012, slower than the 8.9 percent year-on-year growth in the previous quarter.
China is the world's largest oil user and the latest growth data reinforced worries that the nation's appetite for crude could weaken as industrial activity slows.
"The weak GDP data has caused prices to retreat almost immediately, along with other commodities," Justin Harper, market strategist at IG Markets Singapore, told AFP.
China's annual growth slowed to 9.2 percent last year from 10.4 percent in 2010, as turbulence in Europe and the United States hit the export-driven economy.
The government said in March it had cut its economic growth target to 7.5 percent this year, in an official acknowledgement that the economy is slowing.
The fall in oil prices came despite a rise in regional stock markets, which were given some support by news of North Korea's failure to launch a rocket into orbit.
Pyongyang's rocket exploded mid-air before splashing down in the Yellow Sea off South Korea.