A unicellular Rhodophyte was identified by sequencing of its 18S rRNA encoding gene as belonging to the Rhodella violacea specie. With the objective to optimise the production of biomass and exopolysaccharide by this strain, effects of irradiance, pH and temperature on its photosynthetic activity were investigated. In a second time a stoichiometric study of the well-known f/2 medium led to its supplementation in N and P to increase biomass and then exopolysaccharide yields when the strain was cultivated in photobioreactors. The use of optimal conditions of culture (irradiance of 420 mu E/m(2)/s, pH of 8.3 and temperature of 24 degrees C) and f/2 supplemented medium led to significant increases of biomass and exopolysaccharide productions. The structural characterisation of the produced exopolysaccharide revealed that it was sulphated and mainly composed of xylose. The different culture conditions and culture media tested had no significant impact on the structure of produced exopolysaccharides. (c) 2013 Elsevier Ltd. All rights reserved.