Antifungal substances from Pseudomonas aeruginosa (PAFS) are currently under purification, and its partially purified fractions with sporulation suppressing activity and another fraction with activity of inhibiting mycelial growth of Oomycota were investigated. Primary fractions of PAFS, A1, A2, A3, and A6 appeared to contain 2 classes of antifungal substances.First, fractions, A1, A2, and A3 elicit specific suppressive actions in asexual sporulation of ascomycete fungi, mainly by the incomplete development of spores; however, interestingly, these fractions have negligible inhibition in mycelial growth. In contrast, A6 appeared to have a inhibitory activity in mycelial growth of Oomycota. Also antifungal activities of these fractions seem to be persistent as revealed by the impaired germinability of spores which were formed in the regime of this fraction.