medicine for various purposes. Recently, aquatic habitats have increasing been shown to provide a rich source of natural bioactive compounds. Green algae Ulva lactuca is a widespread macro algae occurring at all levels of the intertidal zone, in calm and protected harbours as deep as 10 meters and in northern climates. Many of its nutrients include iron, protein (15%), iodine, vitamins (A, B1, and C) and trace elements. The present study investigated the bioactivity of Ulva lactuca methanolic crude extract and its water fraction. Also we identified on their different bioactive constituents using high performance liquid chromatography technique. Our results showed that methanolic crude extract of Ulva lactuca and its water fraction had phenolic and flavonoid active constituents acting in synergism to increase their bioactivity such as antioxidant, antiinflamatory and antihemolytic activities. Through 15 days, there was no mortality detected among mice injected with Ulva water fraction different doses. Therefore, we could not calculate the LD50 and accounted it as safe agent. Finally we concluded that Ulva water fraction safe to be used in the treatment of oxidative stress and inflammation related disorders.