Marine algae are important sources of phycocolloids like agar, carrageenans and alginates used in industrial applications. Algal polysaccharides have emerged as an important class of bioactive products showing interesting properties. The aim of our study was to evaluate the potential uses as anticoagulant drugs of algal sulphate polysaccharides extracted from Ulva fasciata (Chlorophyta) and Agardhiella subulata (Rhodophyta) collected in Ganzirri Lake (Cape Peloro Lagoon, north-eastern Sicily, Italy). Toxicity of algal extracts through trypan blue test and anticoagulant action measured by activated partial thromboplastin time (APTT), prothrombin time (PT) test has been evaluated. Algal extracts showed to prolong the PT and APTT during the coagulation cascade and to avoid the blood coagulation of samples. Furthermore, the algal extracts lack toxic effects towards cellular metabolism and their productions are relatively at low cost. This permits to consider the algae as the biological source of the future.