Cytotoxic bibenzyls, and germacrane- and pinguisane-type sesquiterpenoids have been isolated from unidentified Indonesian and Tahitian Frullania sp. and Japanese Porella perrottetiana by using a combination of chromatographic methods. The structure activity relationship (SAR) study showed that the presence of a phthalide group in bibenzyls, an alpha-methylene-gamma-lactone in germacrane-type sesquiterpenoids, and beta-hydroxycarbonyl in pinguisane-type sesquiterpenoids play an important role in providing cytotoxic activity against both human promyelocytic leukemia (HL-60) and human pharyngeal squamous carcinoma (KB) cell lines. The structure of each isolated compound was elucidated by using spectroscopic methods and the cytotoxicity was determined by using the WST-8 colorimetric assay.