The Office for National Statistics (ONS) said the consumer price index (CPI) was held back by slower rises in the price of clothes and university fees and cheaper hotel stays.
Downward pressures were offset by rising prices for motor fuels, and by prices for furniture and furnishings.
Economists expected a small uptick from 1.0% to 1.1% last month.
Sterling fell sharply on the news, losing around half a cent against the US dollar.
Tom Stevenson, investment director for personal investing at Fidelity International, said: “Against all expectations, the CPI rose by just 0.9% in the year to October, slightly lower than September’s 1% increase. However, prices are still rising faster than at any time since late 2014. The rise in prices continue to be driven by sterling’s recent weakness which has raised the cost of imported fuel and food.
“Consumers can expect UK inflation to continue rising into next year as the impact of the pound’s slide continues to be felt. The conventional wisdom is that the Bank of England’s 2% inflation target will be left behind in 2017.”
Ben Brettell, senior economist at Hargreaves Lansdown, said: “Today’s surprise fall looks like a blip, as sterling weakness continues to raise the cost of inputs for UK businesses. The cost of raw materials and fuels bought by UK companies jumped at the highest monthly rate on record in October, with total input prices up 4.6% from September.
“It should be only a matter of time before this feeds into higher consumer prices. The Bank of England now expects inflation to hit 2.7% next year, but some analysts are predicting it will reach 4% as sterling weakness pushes up import costs. With wage growth expected to be weak in the wake of the vote to leave the EU, real wages look set to fall next year.”