In vitro studies was conducted to evaluate the effect of seaweed liquid extracts of Caulerpa racemosa (green alga), Sargassum myricocystum (brown alga) and Gracilaria edulis (red alga) at different concentrations of 10, 15, 20, 25 and 30% along with control against the mycelial growth of Fusarium oxysporum f. sp. udum by poison food technique. Result revealed that extract of S. myricocystum showed significant antifungal activity against pathogen followed by G. edulis and C. racemosa. S. myricocystum (30%) extract recorded the lowest mycelial growth (28.1, 33.9, 34.7, 39.4 and 44.3 mm) at 24, 48, 72, 96 and 108 hrs after incubation. Among the antagonists tested against Fusarium oxysporum f.sp. udum, the fungal antagonists Trichoderma viride was found to be most effective in reducing the mycelial growth than the bacterial antagonist Pseudomonas fluorescens. Both the antagonistic of fungi and bacteria has compatability with seaweed extracts in all the concentrations.