Algal polysaccharides, also called phycocolloids, are the main commercial seaweed extracts: their productionfor sale reached 86,100 t over the world in 2009, considering agar, alginates and carrageenans productions(Bixler and Porse 2010). They are mainly used in the agri-food sector, as texturing agents, stabilisers,gel formers of film forming agents. Many other industrial applications exist, as microbiological and electrophoresismedia for agar, use in textile printing and paper coating for alginates and in toothpaste, cosmeticsand pharmaceutics for carrageenans (Bixler and Porse 2010). To our knowledge, their environmental assessmentusing Life Cycle Assessment (LCA) has not been performed yet, despite this large use at industrialscale.We performed the LCA of phycocolloid production including seaweed cultivation. The Recipe method(Goedkoop et al. 2009) was used, with a hierarchist perspective using the ecoinvent v2.2 database and theSimaPro 7.3 software to carry out the impact assessment. The functional unit was to produce 1 kg of hydrocolloid.The study is a prospective for European countries, considering pilot and semi-industrial data fromthe North-Eastern Atlantic zone (data from Aleor, French seaweed producer). Bibliographic data were alsoused for electricity consumption (Mafart 1997). We modeled the production of food-grade phycocolloid,because this use is the main market for phycocolloids (Bixler and Porse 2010). Brown seaweeds are considereddue to their high growth rate potential. In the present study, seaweed was Saccharina latissima, commonlyfound in this area, and reaching high alginate content, with high levels of guluronic to mannuronicacid ratio. It was cultivated on long-lines in coastal waters, after plantlet production in nursery, as describedin Langlois et al. (2012). Seaweeds were treated straight after harvest, with common techniques of sodiumalginate production (McHugh 2003). Seaweed were first washed, crushed and treated with alcohol. Afteracid lixiviation and dewatering, an alkaline extraction was carried out to solubilise alginates, followed bydewatering using filter press. An acid precipitation with blending was then operated, followed by a last dewateringand the addition of sodium carbonate before drying.Contribution analysis results highlight the importance of the sodium alginate production itself (see Fig. 1).On average on every impact categories, the seaweed production accounts for less than 1% of the total impacts,even allowing bioremediation to marine eutrophication thanks to the nutrient uptake offshore. Electricityis the main contributor to environmental impacts for 12 over 18 impact categories analysed, reaching 39%of the total impacts on average. It is followed by the use of chemical (mainly because of hydrochloric acid),accounting for 26% of the total impacts on average. Heat and cooling requirements, wastewater and wastetreatments, and the use of freshwater and mineral filter aid have only secondary impacts compared to them.This work underlines the key elements to improve for an ecodesign of phycocolloids production.