Abstract: At present, there is a need and demand for the development of safe, cheap and effective topical herbal formulations as sun screens. In this context, this study was initiated to evaluate the sunscreen potential of a Sri Lankan salt marshy plant, Salicornia brachiata Roxb (Family: Amaranthaceae; formally Family: Chenopodiacea) in vitro using a UV spectroscopic technique and Mansur equation. Sun Protection Factor (SPF) value was ascertained (which is an index of sun protection activity) using a methanolic extract having a concentration of 2.0 mgmL-1. Methanol soluble fraction of Dermatone® (2.0 mgmL-1), a well known sunscreen cream, was used as the reference agent. The results showed that the plant extract has a markedly high absorbance values (3.0-3.2) at 290-320 nm range with a SPF value of 30.89 (which is a novel finding) whilst the reference agent exhibited a SPF value of 34.23. Phytochemical analysis of the extract showed the presence of flavonoids, tannins, phenols and steroids. It is concluded that a safe, cheap and efficacious topical sun screen formulation could be developed from salt marshy plant S. brachiata.