The rhamnolipids produced by Pseudomonas aeruginosa strains are often a mixture of several homologues. Up to seven (R2C10C10 + R1C10C10 + R2C10C12 + R1C10C12 + R1C12:1C10 + R1C12:2 + R1C8:2)have been identified in cultures of P. aeruginosa AT10 from soybean oil refinery wastes. This study deals with the production, purification, and identification of rhamnolipids in the mixture (M-7), as well as their physical and chemical characterization and the evaluation of their antimicrobial properties. The surface tension decreases to 26.8 mN/m and the critical micelle concentration value to 1.2 x 10(2) mg/L. These molecules show excellent antifungal properties against Aspergillus niger and Gliocadium virens (16 mug/mL) and C. globosum, P. crysogenun, and A. pullulans (32 mug/mL), whereas the growth of the phytopathogenic fungi B. Cinerea and R. solani was inhibited at 18 mug/mL.