The aims of this study are to isolate and identify active compounds of mangrove plants Rhizophora mucronata Lamk bark extract obtained from the mangrove forest of Kendari Bay, Southeast Sulawesi Province Indonesia and study their cytotoxic activities against cervical cancer (HeLa) cell line. The isolation and purification of the compounds were carried out under several chromatography methods, including thin layer chromatography, vacuum liquid chromatography and radial chromatography with silica gel as adsorbent and various solvents mixture as an eluent. Elucidation of the structure of the isolated compounds was done based on FTIR, 1 H-NMR, 13 C-NMR (1D and 2D) spectroscopic data and confirmed with an existed data from literatures. From this research, it was obtained two pure compounds, α-amyrin (1) and β-sitosterol (2). The isolation of this α-amyrin was firstly reported so far from the bark of this plant. Cytotoxic activities, marks by an IC50 value, of both α-amyrin and β-sitosterol are 804.762 ± 0.22 μg/mL and 353.871 ± 0.53 μg/mL respectively and shows that cytotoxic of β-sitosterol is stronger than α-amyrin.