Abstract: This study was directed to evaluate the in vitro sunscreen potential of Sri Lankan medicinal plant - Flueggealeucopyrus (In Sinhala – Katupila, In Tamil – Mulluppulatti) (Family: Phyllanthaceae)using in vitro UV spectroscopic techniques and Mansur equation with 0.2 and 0.4 mg mL-1 methanolic extracts of the plant leaves. A methanol soluble fraction of Dermatone® (0.2 and 0.4 mg mL-1) was used as the reference agent. The results revealed high absorbance levels of methanolic extract of the plant leaves at 290-320 nm (UVB) range and SPF (Sun Protection Factor) was determined as 14.63/ 27.04 respectively for the 0.2mg mL-1 and 0.4 mg mL-1 concentrations, which is a novel finding, while Dermatone® exhibited a SPF value of 14.03/ 25.32. It can be concluded that F.leucopyrus leaves have a high sun protection activity which is possibly mediated via antioxidant activity of existing phytochemicals; phenols, flavonoids, alkaloids and tannins which was revealed by the phytochemical screening.