The phytochemistry and biological activity of four rare Balanophora species (B. subcupularis P.C. Tam (BS), B. tobiracola Makino (BT), B. fungosa var. globosa (Jungh.) B.Hansen (BFG), and B. fungosa subsp. indica (Arn.) B.Hansen (BFI)) growing in Vietnam have been studied. The six pentacyclic triterpenoids including β-amyrin, βamyrone, lupenone, lupeol, β-amyrin acetate, and lupeol acetate could be identified in all GC-MS chromatograms of four species but very different area percentage. The chemical investigation of B. subcupularis and B. tobiracola led to the isolation of coniferyl aldehyde, gallic acid, cinnamic acid, and caffeic acid. Gallic acid and coniferyl aldehyde were isolated from B. subcupularis for the first time, Among isolated compounds, coniferyl aldehyde showed moderate cytotoxicity activity at cancer cell lines MCF-7, A549, Hep3B, and PC3 at the concentration of 100 µg/ml (CS% = 24.05 – 46.61%). Besides, this compound also significantly inhibited NO production (I% = 101.96 and 114.29 at two respectively concentrations of 30 µg/ml and 100 µg/ml).