Abstract: The antimicrobial actives of Plocamium telfairiae Harv were fractioned from its crude extract with different solvents and were tested to against Pseudomnas aeruginosa and Trichoderma viede.The result indicated that the chloroform and ethyl acetate fractions exhibited antibacterial activities and their antibacterial degrees were stronger than it of fractions obtained with other solvents.The inhibition zone were 14.3mm and 8mm diameter at the fraction concentration 100 mg·mL-1, respectively.The chloroform and petroleum ether fractions showed antifungal activities to against the mycelium growth of Trichoderma viede and the inhibition rate was 54.57% and 36.55%after 72hincubation, respectively.The antifungal activity of two fractions was stronger than it of fractions obtained with other solvents.The ethyl acetate fraction of Plocamium telfairiae Harv extract was again fractioned twice through silicone gel column to obtain compounds D.This compounds were identified and showed the antimicrobial properties to against Pseudomnas aeruginosa (13mm diameter with 100mg·mL-1) and to inhibit Trichoderma viede mycelium growth (48.53%, with 50 mg·mL-1) respectively.The result of GC-MS assay showed that the antimicrobial compounds D determined preliminarily could be as 4-hydroxy-benzaldehyde.However, the further purification for antimicrobial compounds D is required to identify their active compound.