Abstract: To study the chemical constituents and antimicrobial compounds of Plocamium telfairiae Harv., the silica gel column, SephadexLH-20 column and thin layer chromatographic techniques were applied to separate and purify the compounds. structures of compounds were confirmed by the data of mass spectrum and spectral. Four compounds were isolated from the ethanol extract of Plocamium telfairiae Harv.. Then these compounds were identified by GC-MS, 1H-NMR and 13C-NMR spectral analysis. Four compounds were identified as n-hexadecanoic acid, octadecanoic acid, 4-hydroxybenzoic acid, dioctyl phthalate. The 4-hydroxybenzoic acid was an antimicrobial compounds from ethanol extract of Plocamium telfairiae Harv..