Tunicates, a group of marine animals, have been attracted a lot of attention in medical application, food market, water pollution issues and exploited in the food industry. However, limited knowledge of their chemical composition and nutritional profiles prohibited further application. In this study, three common colonial tunicate species, Polylinum indicum, Polylinum nudum and P. saturnium were subjected to comprehensive composition analysis in terms of moisture, protein, lipids, cellulose, ash, amino acids, fatty acids, non-cellulose carbohydrates and minerals. In addition, antimicrobial activity of the solvent extract of these ascidians was also studied. All the three species had low carbohydrate content, and protein and fat were their main components. Having high quality protein content, these species could be excellent sources of nutritive ingredients. Among amino acids, glutamate, aspartic acid, alanine, leucine and lysine were present at high levels in the ascidians, while the major elements present were sodium, chloride, magnesium and phosphorous. The selected species demonstrated balanced essential to non-essential amino acids ratio. Among polyunsaturated fatty acids, eicosapentaenoic acid and docosahexaenoic acid were found to be prominent. Higher content of vitamin A and vitamin B3 in Polyclinum saturnium signified their importance in preventing osteoporosis. The heavy metal contents such as lead, copper, cadmium and nickel were found to present below the recommended level. These species exhibited potent antibacterial activity against several bacterial pathogens. Overall, the results indicate that the chosen species of ascidians can be good sources of high quality protein, lipid, and essential elements. Toxic metals were below threshold limits of recommended standards for human consumption. These species could have been utilized as an alternate source for food supplements.