Abstract: This study wasaimed at investigating the sun protective activities of leaves of three Sri Lankan croton plants, Codiaeumvariegatum,C.variegatum type 1 and C.variegatum type 2 (family :Euphorbiaceae) in vitro using UV spectroscopic technique and Mansur equation. Sun Protection Factor (SPF) values were determined (which is an index of sun protection activity) using 0.2 mg/mL of methanolic crude extract of each plant. Dermatone ® and Suncote® were used as reference agents. Phytochemical profile of C.variegatum was also investigated using standard protocols and TLC analysis. The results showed that crude extracts of leaves of C.variegatum type 1 and C.variegatum type 2 exhibit mild sun protective activity,( SPF values of 6.39± 0.08 and 8.48± 0.10 respectively) whilst C.variegatum has high SPF value (18.25 ± 0.22). And also reference agents Dermatone® and Suncote®had high SPF values (25.05 ± 0.33 and 27.54 ± 0.35 respectively). Flavonoid fraction of C.variegatum from TLC studies displayed a higher SPF value (25.92 ± 0.32) which is higher than the SPF value of its crude extract. Phytochemical screening of C.variegatum crude extract showed the presence of flavonoids, tannins, phenols, alkaloids and diterpenes. It is concluded that the sun protection activity of C.variegatumis mediated primarily by flavonoids via its antioxidant activity and this plant is a promising source to develop a cheap, consumer friendlyand efficacious sunscreen formulation.