The economic performance of organic dairy farms, especially during the transitional period, is not consensus in economics studies, depending on the method used, the type of indicators, the nature and scale of the performance indicator, the geographical location. We compare the economic and financial performance of both conventional and organic dairy farms based on a mixed effect panel data model estimated on 1,016 farm micro-data collected between 2007and 2018 in two departments of Brittany. As in other studies, we find that the herd size influences positively all economic and financial indicators. Even if the growth in assets is heterogeneous among organic farms, it is higher than in other farms, which decreases their return on assets. Finally, even if they share the same objective of food autonomy and sparing variable expenses, dairy farms based on grassland production system do not exhibit the same performance dynamics as organic farms.