Marine algae are valuable sources of structurally diverse bioactive compounds, among them, the group of sulfated polysaccharides (SPs). As an example of SPs, it could be cited the fucoidans in brown algae, carrageenans in red algae and ulvans in green algae. Since the past decades, SPs have been extracted from algae and evaluated in respect to their beneficial biological activities such as anti-inflammatory, antioxidative, antimicrobial, anticoagulant, antithrombotic, immunological and anticancer. This review deals with the presentation of natively bioactive SPs structural features in addition to already employed approaches of SPs structure modifications, such as chemical and physical methods. Moreover, this article presents the advantages and the importance of using enzymatic methods during SPs modification, and particularly, the use of microorganisms as enzymes sources. Enzymes such as hydrolases/glycosidases (e.g. fucoidanase, fucosidase, agarase and carrageenase), lyases, sulfotransferases and sulfatases could be used for this purpose. It has been shown that more studies are necessary to obtain/identify opportunities to create novel, or to intensify, SPs biological properties. Considering the advantages in the use of microbial enzymes in biotransformation processes, studies related to the modification of SPs by microorganisms should be stimulated. (C) 2016 Elsevier Ltd. All rights reserved.