Six new meroterpenoids, diplomeroterpenoids A-F (1-6), two new chalcone-lignoids, diplochalcolins A and B (7, 8), and 13 known compounds were isolated from the root extract of Mimosa diplotricha. Diplomeroterpenoids A-F consist of a 4H-chromen-4-one and a diterpenoid unit, and their absolute configurations were determined by X-ray crystallographic analysis. Compounds 1-3 and 5 showed potent inhibitory activity on protein farnesyl transferase, with IC50 values from 5.0 to 8.5 μM. Compound 1 showed antiproliferative activity against human hepatoblastoma HepG2 cells with a GI50 value of approximately 8.6 μM.