Two kinds of glycolipids (R-l and R-2) were produced in the culture media by several strains of Pseudomonas aeruginosa when grown on n paraffin (mixture of C₁₂, C₁₃. and C₁₄ fractions). These compounds were isolated through the extraction of the culture broth with ethylacetate and the chromatography on silicic acid column. On the basis of chemical analysis, these lipids were characterized as 2-O-α-L-rhamnopyranosyl-α-L-rhamnopyranosyl-β- hydroxydecanoyl-β-hydroxydecanoate (R-l) and L-α-rhamnopyranosyl-β- hydroxydecanoyl-β-hydroxydecanoate (R-2). Bactericidal activity of R-2 which is postulated to be a precursor of R-1 was remarked against grampositive bacteria. Further, these compounds also demonstrated mycoplasmacidal and antiviral activities in vitro.