The annual rate of house price growth slowed in September to 9.4% from 11% the month before, the Nationwide says.
On a monthly basis, prices were down by 0.2% – the first time that figure has fallen since April 2013.
Even though the monthly figures show house prices falling, they still rose by 1.5% over the quarter.
Robert Gardner, the Nationwide’s chief economist, said: “While September saw a slowing in house price growth, the picture on a quarterly basis (July, August and September combined) was still relatively strong, with all thirteen UK regions recording annual price gains.”
Mr Gardner said that prices were expected to continue rising in the final months of the year, but this could be at a slower rate.