The present experiment was conducted at the Fruit Research and Development Institute Horana, Sri Lanka, from 2020 to 2021 to evaluate the proximate composition, antioxidant activity, ascorbic acid and total phenolic content of five underutilized fruits, namely Namnam, Lovi, Roseapple, Pumello and Sapota using Association of Official Agricultural Chemists (AOAC) methods. The parameters determined were moisture, crude fiber, crude fat, sugar, antioxidant activity, total phenolic content, titratable acidity, pH, total soluble solids and ascorbic acid. Rose apple and Namnam fruits recorded the highest (91.47%) and the lowest (68.87%) moisture content, respectively. The Pumello fruit exhibited the lowest fat, crude fiber, total sugar, non–reducing sugar and reducing sugar contents with the values of 0.01%, 1.33%, 005%, 0.03%, and 0.02%, respectively. Sapota reported the highest fat, total soluble solids and pH values of 1.33%, 16%, and 4.74%, respectively. Roseapple recorded the highest crude fiber (5.59%) and the total sugar content (0.81%), while Lovi showed the lowest pH (2.29) and highest titratable acid content (2.01%) Pumello had the highest ascorbic acid concentration, whereas Lovi had the lowest value. Pumello and Namnam demonstrated the lowest IC50 value (0.03). Sapota and Roseapple had the highest (20.49) and lowest (2.16) total phenolic content. The study emphasizes the diverse nutritional elements in these underutilized fruits, highlighting their potential as valuable sources of supplementary nutrients.