The present study aims to develop the operating conditions to produce ash from marine biomass i.e. Sargassum seaweed in order to consider their ash as pozzolanic materials. An experimental design is used to determine the most significant parameters of the ash elaboration. The parameters of the experimental design are calcination temperature (600 and 700 ◦C), granulometry of raw biomass (diameter D < 0.4 mm and 0.4 mm < D < 1 mm) and content by mass of algae (67 wt% of Sargassum fluitans and 100 wt% of Sargassum fluitans). The influence of these parameters on the yield of calcination, specific density, loss on ignition of ash and pozzolanic activity of ash are studied. At the same time, texture and a number of oxides in ash are observed by scanning electron microscopy. The first results show that in order to obtain light ash, a mixture of Sargassum (67% by mass of Sargassum fluitans + 33% by mass of Sargassum natans) of diameter (0.4 mm < diameter <1 mm) should be burnt at 600 ◦C for 3 h. In the second part, it appears that the morphological and thermal degradation characteristics of the Sargassum algae ash are similar to pozzolanic materials ones. Nevertheless, Chapelle tests, chemical composition and structural surface, crystallinity show that the Sargassum algae ash is not a pozzolanic-like material.