Across the UK there were 96,910 residential transactions in June, on a seasonally-adjusted basis.
That is a fall of 3.3% on May's number, and the lowest total since October 2016.
The figures, from HM Revenue and Customs (HMRC), represent a small annual rise, up 1% in comparison with June 2016.
However, last summer's sales were depressed by the introduction of additional stamp duty rates in April.
It is also the first time this year that the number of transactions has fallen below 100,000 a month.
Property experts think the figures give a more accurate indication of the health of the market than house prices.
"These figures are disappointing as we would have expected them to be much higher bearing in mind the turmoil in the market this time last year following the introduction of the stamp duty surcharge," said Jeremy Leaf, a north London estate agent.
Where can I afford to live?
The number of homes being bought and sold has fallen for the third month in a row, according to government figures.