Retail Price Index (RPI) inflation fell from 3.2 per cent to 2.9 per cent.
This follows a rise in July from 2.4 per cent to 2.6 per cent.
This month's figures will be positive for the Bank of England as it works towards its target of two per cent inflation.
The largest downward pressure came from furniture, household equipment, household services and clothing and footwear. Upward pressures came mainly from transport which rose 1.3 per cent.
For the RPI, which includes mortgage payments, largest downward pressures came from household goods, clothing and footwear and food. The only upward pressures came from fares and travel costs.
The CPI rose by 0.5 per cent between July and August 2012 compared with a rise of 0.6 per cent a year ago.
Between August 2011 and August 2012, the CPI rose by 2.5 per cent.
Since April 2011, the CPI is the index used to calculate tax benefits, tax credits and public service pensions.
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