Pterolobium macropterum, which belongs to the family Leguminosae, is a medicinal plant that is found throughout China, Bhutan, India, Indonesia, and Southeast Asia. In Thailand, this plant has been used to treat toothache and fever and to promote wound healing.7 In northeast Thailand, the plant is known as “nam kra jai”. In a study on the isolation of cytotoxic agents against CCA from natural sources, it was observed that crude extracts (hexanes, EtOAc, and MeOH) of the root bark of P. macropterum exhibited cytotoxicity with IC50 values ranging between 9 and 45 μg/mL. Thus, investigating the root bark of P. macropterum resulted in the isolation of four new cassane diterpenoids (1−4) and a new cadinane derivative (5). All of the pure compounds were evaluated for cytotoxicity against the CCA, KKU-M136, KKU-M159, and KKU-M216 cell lines.