Algae are a group of organisms, Thallophytes, containing specific bioactive compounds (i.e. brominated phenols, heterocyclic oxygen compounds, sterols, terpenes, polysaccharides). Their excessive growth has negative consequences on marine organisms; on the other hand, they have a crucial role in food, pharmaceuticals, cosmetics, agriculture. In this paper were studied the main physical-chemical characteristics correlated with the biological specificity of three species of multicellular algae, Enteromorpha intestinalis and Ulva rigida (green), Ceramium rubrum (red), frequently encountered along the Romanian Black Sea coast. Generally mixtures of thallophytes algae from the Black Sea were collected, processed and characterized. Density, pH, conductivity, anions, loss on drying, ash, total nitrogen, protein, lipids, carbohydrates, carotenoids were determined. The results emphasized the possibility of using these marine resources as biofertilizer in agriculture.