Plant populations at range edges may exhibit reduction of performances and fitness. In the case of biological invasions, such a reduction could be associated with a slowing down of the spread and explain the non-naturalization of a species outside its present invasion range. Common ragweed (Ambrosia artemisiifolia L.) is an ideal model to investigate such processes, since it is invasive in France but not naturalized in northern countries, such as Belgium and the Netherlands. In this study, we test if the performances of ragweed populations vary among different invasion zones. Three populations were selected in each of four invasion zones in Western Europe: 1) French invasion area; 2) northern and 3) southern invasion edges; and 4) outside the invasion area (Belgium and Netherlands). Field performances (growth, reproduction, stress resistance) were recorded on 25 plants per population. Furthermore, the competition by the native flora was assessed around each plant. Generalized Linear Models were used to compare performance among invasion zones and populations, with competition as covariate. Regressions were also performed to assess the influence of climatic data on population performances. No evidence of decreasing performances was found at the edges of the invasion area, neither outside of it, suggesting that the invasion front has the potential to keep going northwards. Competition by native flora had a significant impact on stress resistance, but did not decrease reproduction or growth. These results are discussed in the light of other ongoing experiments in Belgium.