Sri Lanka has been identified as one of the world’s biodiversity hotspots with a rich array of fruits; however, most of them remain underutilized. The present study was carried out to investigate the nutritional composition and to assess the bioactivity of six underutilized fruits collected from three provinces of Sri Lanka. The selected fruit species were Màdan (Syzygium cumini), Maha Karamba (Carissa carandas), Himbutu (Salacia chinensis), Ugurassa (Flacourtia indica), Barbados cherry (Malpighia emarginata), and Ceylon gooseberry (Dovyalis hebecarpa). The proximate composition, total dietary fiber content, mineral content, total phenolic content, and vanillin contents were determined using standard methods. The antioxidant activity of methanolic extracts of fruits was assessed using FRAP and DPPH assays. Uguressa extract exhibited the highest dietary fiber content (12.25 ± 0.29 of fresh fruit weight) while the lowest was observed in Barbados cherry (6.01 ± 1.10 g/100 g). The total phenolic content (TPC) of fruits ranged from 6.8 ± 0.4 to 10.3 ± 0.3 milligram gallic acid equivalents/g fruit. Barbados cherry showed the highest antioxidant activity (AOA) as measured by FRAP (0.022 ± 0.003 mM Fe 2+/g fruit) and the highest vanillin content (2.4 mg/kg). The highest potassium (434.60 ± 0.36 mg/kg), phosphorous (16.69 ± 0.46), and calcium contents (23.43 ± 0.45) were observed in Uguressa. Màdan had the highest content of magnesium (13.25 ± 0.38 mg/kg), sodium (5.28 ± 0.30), iron (0.65 ± 0.12 mg/kg), and aluminum (1.15 ± 0.16 mg/kg). The highest manganese content (0.98 ± 0.18 mg/kg) was observed in Himbutu while the highest copper content was found in Uguressa (0.11 ± 0.04 mg/kg) and Maha Karamba (0.11 ± 0.03 mg/kg). The study reveals that six underutilized fruits tested possess high nutritional value and are rich in antioxidant activity.