The present work aims to study the fertilizing power of the invasive algae Sargassum spp. in order to initiate their valorization as organic fertilizer in agriculture. The experimental device is composed of two pits of dimensions 1m x 1m with a depth of 1m, filled with 100 kg of rinsed and dried Sargassum spp. The pit intended for vermicomposting received 1 week after the beginning of the experiment 1.8 kg of mature earthworms (Eudrilus eugenia). The moisture content of the pits was maintained at 60-70%. Samples were taken at the beginning of the experiment and every 4 weeks for 4 months, for analysis at the PETROCI-Côte d'Ivoire laboratory to determine the initial physical and chemical parameters and during the decomposition of Sargassum spp. Regarding the physical and chemical characteristics of the residues, some compounds such as phosphorus (20315 ppm) and potassium (24488.8 ppm) have very high values with a slightly basic pH (7.7). During decomposition, nutrients are released and their content increases rapidly in the vermicompost before decreasing generally until the end of the experiment. The residues of Sargassum spp. considered as waste by the populations contain important nutrients (C, N, P, K, ….), thus possessing an important fertilizing power potentially favourable to an organic agriculture.