The purpose of this study is to examine the qualitative, quantitative, and in vitro anticancer properties of Ulva lactuca. To achieve this, we utilized five solvent extracts, and our findings revealed that both methanolic and aqueous extracts contained phytochemical compounds such as alkaloids, phenols, flavonoids, tannins, saponins, terpenoids, steroids, carbohydrates, glycosides, and proteins. However, the ethanol, ethyl acetate, and chloroform extracts of Ulva lactuca lacked flavonoids. Moreover, the methanolic extract of Ulva lactuca exhibited higher levels of alkaloids, total phenols, terpenoids, steroids, and tannins than the other extracts, as determined by quantitative analysis. Subsequently, we assessed the anticancer properties of the methanolic extract using the lung cancer (A549) cell line and observed potent cytotoxic activity via MTT assay. In light of these results, it is evident that Ulva lactuca seaweed extracts hold promise as an effective alternative in cancer treatment.