Preliminary unadjusted data showed the economy increased 1.2% in the second quarter from the same period of 2011. In seasonally adjusted data, the annual growth was 1.7%.
For the first six months of 2012, Romanian GDP grew at an annualized rate of 0.8%, INS said. The adjusted data showed the economy expanded 1.2% in January through June.
Detailed figures for the second-quarter GDP are due for release September 6.
The Romanian government last week revised down its economic growth forecast to 1.2% in 2012 from 1.5% previously, saying it expected a weaker contribution from agriculture than previously envisaged after a large part of the crops were damaged by drought.