Support from the opposition meant there had been no doubt Germany would okay new powers for the European Financial Stability Facility (EFSF), which some countries like Finland have ratified but others, including Slovakia, are disputing.
The Bundestag's (lower house of parliament) deputy speaker Wolfgang Thierse said 523 lawmakers had voted for the bill, 85 against with only three had abstentions.
If a breakdown of votes expected take up to an hour more shows the bill only got through thanks to the centre-left opposition, it would undermine the conservative chancellor's ability to pilot fresh measures to combat the euro crisis.
Merkel had tried to assure her coalition that taxpayers' money would not be wasted by supporting bailout measures - but she could not rule out that the money might be written off if, as financial markets increasingly fear, Greece defaults.
Germany will shoulder up to €211bn of the fund's €440bn euros worth of guarantees, but critics fear it is already clear this will not be enough and taxpayers will be asked for more.
That impression was reinforced by talk at the International Monetary Fund last weekend of the need to beef up the EFSF even more - on top of the extra powers decided by European leaders in July - by leveraging its capital and bring forward the permanent scheme supposed to replace it in mid-2013.