Since 2011, Caribbean beaches have been flooded by massive quantities of pelagic Sargassum, causing environmental, health and financial problems. The use of Sargassum ash as a stabilizer in the manufacture of bricks can help mitigate the economic impact of Sargassum grounding by adding value. This study assesses the effect of the Pelagic Sargassum algae desalination process on the properties of the biomass as well as the potential application of their ash as a stabilizer in soil-based bricks. Fresh Sargassum algae was subjected to two cycles of immersion in water, then calcined under different conditions (temperature and time) and characterized. The desalinated Sargassum ash (SA) was used to partially replace cement in the stabilization of earth bricks. Characterization of raw and desalted Sargassum shows a reduction in ash content from 28.44 to 17.25% after desalination. Furthermore, the thermo gravimetric analysis show a slight reduction in the initial degradation temperature between 204 and 602 °C, which is associated with a reduction in the amount of residual char from 35% to 27%. The results of the XRF analysis of the SA showed a very low alumiosilica content (SiO 3 +Al 2 O 3 < 4%), but a significant increase in CaO content after desalination from 21.96 to 50.17%. The XRD results of the SA are consistent with the XRF analysis which reveals that the desalination process significantly increased the CaCO 3 content from 19 to 67%, while KCl decreased significantly from 26 to 8%. Furthermore, the characterization of the composites reveal that partial substitution of 10 wt.% cement by SA calcined at 700 °C for 2 hours has no significant effect on water absorption, density, compressive strength and chemical composition of earth bricks. This material could help reduce pollution linked to the decomposition of sargassum on Caribbean coasts and beaches, as well as greenhouse gas emissions linked to cement production.