The ECB also reduced the interest rate on its deposit facility to 0.5 percent and the rate on the marginal lending facility to 2.0 percent.
ECB President Mario Draghi will explain the Governing Council's decision at a 1330 GMT news conference -- his first at a monetary policy meeting after taking over the reins on Tuesday from Jean-Claude Trichet.
The cut marked a change in policy course after the ECB increased its rates in July and April, when it became the first major central bank to hike after the intensification of the financial crisis. Markets are now looking for hints whether the ECB is preparing to cut rates again next month.
Attention will also focus on other changes in the central bank's policy after the change of guard, especially whether its government bond program will be boosted.
(Reporting by Sakari Suoninen)