Montri, N.1 and Suwanajan, J1 Abstract The effects of different concentrations of aqueous extract of Melaleuca cajuputi Powell at 100, 200, 400 and 800 mgL-1 on growth of Fusarium oxysporum, Collectotricum gleosporides, Phytopthora parasitica and Pythium deliense in Potato Dextrose Agar (PDA) were investigated. The result found that all concentrations of M. cajuputi aqueous extract could inhibit growth of those pathogenic fungi. The percentage of fungi inhibition was increased gradually with higher concentrations. The hundred percent of growth inhibition of Phy. Parasitica and P. deliense were found in 400 and 800 mgL-1 treatments at 4 and 1 days of culture. While the highest percentage of growth inhibition at 87.84 and 86.16 % was achieved in 800 mgL-1 treatment for F. oxysorum and C. gloeosporiodes after 5 and 9 days respectively.