Farming systems have been strongly modified during the second part of the XXth century. These evolutions of husbandries have induced changes of the arable flora which need to be quantified. This paper analyses changes in the weed flora in 158 fields that were surveyed in 1968/76 and 2005/2006. Results show that during the 30 last years, the composition of the weed flora has been strongly modified with only half of the species observed common to both surveys. In addition, the frequency of occurrence and average density of species that were common to both surveys has declined drastically. One exception is the increase of species mostly related to rapeseed crops. Species that were already rare 30 years ago have continued to decline