Foods enriched with nutritional compounds and biological activities, especially antioxidants, are considered healthier for human and/or animal consumption. Seaweeds are rich sources of biologically active metabolites and are used as functional foods. In this study, proximate compositions, physicobiochemical characteristics and oil oxidative stability were analyzed for 15 abundant tropical seaweeds (four green—Acrosiphonia orientalis,Caulerpa scalpelliformis,Ulva fasciata,Ulva lactuca; six brown—Iyengaria stellata,Lobophora variegate,Padina boergesenii,Sargassum linearifolium,Spatoglossum asperum,Stoechospermum marginatum; and five red—Amphiroa anceps,Grateloupia indica,Halymenia porphyriformis,Scinaia carnosa,Solieria chordalis). All seaweeds were analyzed for the proximate composition, including moisture content, ash content, total sugar content, total proteins, total lipids, crude fiber, carotenoid content, total chlorophyll content, proline, iodine content, nitrogen-free extract, total phenolic content and total flavonoid content. Green seaweeds showed higher nutritional proximate composition, followed by brown and red seaweeds. Among the different seaweeds,Ulva,Caulerpa,Sargassum,SpatoglossumandAmphiroashowed high nutritional proximate composition compared to other seaweeds. High cation scavenging, free radical scavenging and total reducing activities were observed forAcrosiphonia,Caulerpa,Ulva,Sargassum,SpatoglossumandIyengaria. It was also observed that 15 tropical seaweeds contained negligible amounts of antinutritional compounds, including tannic acid, phytic acid, saponins, alkaloids and terpenoids. Nutritionally, green and brown seaweeds provided higher sources of energy (150–300 calories per 100 g) compared to red seaweeds (80–165 calories per 100 g). Additionally, this study also confirmed that tropical seaweeds improved the oxidative stability of food oils and, therefore, might be recommended as natural antioxidant additives. The overall results confirm that tropical seaweeds are potential sources of nutrition and antioxidants and may be explored as functional food, dietary supplementation or animal feed. Additionally, they may also be explored as food supplements for fortifying food products, as food toppings or for garnishing and seasoning foods. However, a human or animal toxicity analysis is required before any conclusive recommendation for daily food or feed intake can be made.