The Sun's circulation fell by 5.2 per cent to 3,278,068 while the Daily Mirror's was down by 8.9 per cent to 1,770,407.
Only The Independent and The Times among the dailies managed to increase their year-on-year circulation, a sign that going compact has helped build sales.
The Independent posted its 13th successive monthly rise, adding 13 per cent to its newsstand sale to reach 266,038, while The Times was up 4 per cent to 656,462.
Their rivals The Daily Telegraph and The Guardian fared less well. However, The Telegraph's circulation fell just 1 per cent to 904,366, while The Guardian posted a monthly increase to 378,426, though this was still down 3.6 per cent year on year.
Among the Sunday titles, the mid-market was up slightly, with The Mail on Sunday and the Sunday Express increasing circulations. The Independent on Sunday and the Sunday Mirror also posted small rises but every other title was down.
The Scotsman, which went compact in August, suffered a 0.8 per cent fall to 69,626. However, this is an improvement on previous months.