Jayshree, et al.: Microalgae: Effective Health MediatorsAlgae are rich sources of structurally novel and biologically active metabolites. Primary and secondary metabolites produced by these organisms have drawn interest of the pharmaceutical industries. In this regard we have put forth an investigation to evaluate phenolic and flavonoid content in methanol extract of fresh algal biomass followed by antioxidant, antimicrobial and anticancer activities. Determination of total phenol and flavonoid content was followed by the 2,2-diphenyl-1-picrylhydrazyl radicals scavenging, phosphomolybdate and reducing power assay for evaluating antioxidant potency. Agar well diffusion method for antibacterial activity and trypan blue test along with MTT assay was done for anticancer activity. Among two microalgae, Chlorella vulgaris had efficiently high amount of total phenol and flavonoid content. Chlorella vulgaris is a single-celled eukaryotic green micro algae, known to be first form of a plant with a well-defined nucleus emerged over 2 billion years ago [1] . Chlorella contains the highest amount of chlorophyll of any known plant. Chlamydomonas reinhardtii, another unicellular algae though not much explored as nutrient supplement; it is well known model organism with its three genomes (nuclear, plastidial and mitochondrial) completely sequenced [2] . It finds its application mostly in molecular biology especially in studies involving flagellar motility, chloroplast dynamics, biogenesis and genetics [3] . C. vulgaris is well determined nutrientdense superfood containing 60% protein, 18 amino acids, 20 vitamins and minerals like iron, calcium, potassium, magnesium and phosphorous [4] . One of its unique properties is a phytonutrient called Chlorella Growth Factor [1] . These two microalgae are known for high volume production of β-carotene.Besides being food supplements microalgae, Chlorella sp., Chlamydomonas sp. have been proved to have antibacterial activity in vitro against both Gram positive and Gram negative bacteria [5] . The production of extracellular antibiotic metabolites by marine algae has been well studied in recent years. They are also been reported that a wide range of antifungal activities were obtained from extracts of green microalgae [6] . Eventually, microalgae are almost an untapped resource of natural antioxidants due to their enormous biodiversity, much more diverse than higher plants. They contain various biologically active compounds that are been used as source of food, feed and medicine [7] . Microalgae are