Total Renault sales were down 11.7 percent in October compared with a year ago, on an equal basis of 21 working days, while those of PSA Peugeot Citroen fell 3.0 percent.
DaimlerChrysler posted an 11.9 percent rise, with the Mercedes brand up 24.8 percent, while sales for the Fiat group dropped 21.3 percent.
A spokeswoman for Renault said the October sales were down because prospective buyers were waiting for the launch of the new Clio III. The group was not trying to match the price cuts offered by some rivals, she added.
"The Clio is an important model in our line-up, so that had a clear impact. But we have decided to prefer profitability over sales volume, and that also has an impact because there have been some aggressive price cuts since this summer by a number of our competitors," the spokeswoman said.
Renault's big-volume Megane series of mid-sized cars is also near the halfway point in its life cycle, which depresses sales.
General Motors suffered a 19.9 percent fall in October, with Opel down 21.4 percent, while Ford had 14.3 percent lower sales.
Total sales were 159,693 in the month and 1,726,442 in the year so far. "This is the worst October for six years, and it reflects a morose economic situation and a difficult car market," CCFA spokesman Jean-Pierre Mercier said.