Two sesquiterpene hydroquinones, zonarol and isozonarol, together with neophytadiene have been isolated from the marine brown alga Dictyopteris undulata (= zonarioides).The structure of the compounds were determined by spectroscopic methods. This is the first report of neophytadiene isolation from this species. Zonarol showed significant antimycobacterial activity against Mycobacterium marinum.