SPIRULINA is aquatic and photosynthetic blue green algae and it is a good source of c-phycocyanin pigments. It is widely utilized as food supplement because it contains significant amount of proteins. This investigation is an effort to study some of medicinal applications of S. platensis such as antioxidant capacity, antimicrobial, cholesterol- reduction and anticancer. Antimicrobial activity of methanol, acetone, chloroform and petroleum ether extracts of dried S. platensis was assayed against two fungi (Aspergillus flavus and Aspergillus niger) and four bacterial species (Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Salmonella typhimurium). The S. platensis extracts exhibited significant activity against all tested bacteria and fungi. The highest inhibition zone (1.35 ±0.04cm) was observed in acetone extract against S. typhimurium. While, petroleum ether extract of S. platensis was recorded the minimum activities of all tested antimicrobial and the lowest inhibition zone against Staphylococcus aureus (0.52±0.01cm). The antioxidant potential of different solvent extracts clearly that acetone extract of S. platensis showed highest percentage of DPPH (2, 2 diphenyl-1- picrylhydrazyl) scavenging activity (75%) and highest values of phenolic contents (0.562mg/g DW). S. platensis displayed anticancer activity due to the productions of phycocyanin, allophycocyanin and other valuable products. Calf Serum was used to evaluate the potentiality of various S. platensis extracts to control the tumor effects in vitro. The cell proliferation assay showed that petroleum ether extract at a concentration of 125 μg ml^-1 for 24hrs, significantly inhibited the growth of the Fetal Calf tumor cells (13% viability).