Objective: Isolation of compounds from Dendrobium williamsonii and evaluation of each isolates for its free radical scavenging, antiherpetic and cytotoxic activities. Results: Six phenolic compounds were isolated including tetratriacontanyltrans-p-coumarate (1), trans-docosanoylferulate (2), 3,3′-dihydroxy-4,5-dimethoxybibenzyl (3), moscatilin (4), apigenin (5) and vanillic acid (6). Among these isolates, compounds 3, 4 and 5 exhibited recognizable DPPH free radical scavenging potential.Only 3 exhibited weak activity against Herpes simplex virus, whereas 3 and 4 showed cytotoxicity against KB and MCF-7 cancer cells. Conclusion: This study is the first report on the chemical and biological properties of D. williamsonii.Compounds 3, 4 and 5 are responsible for free radical scavenging activity of this plant. Compound 4 showed the strongest cytotoxic effect on KB cancer cells.