Hydroxy fatty acids have gained important attentions because of their special properties such as higher viscosity and reactivity compared with other non-hydroxy fatty acids. Previously we reported that a novel bacterial strain Pseudomonas aeruginosa PR3 converted linoleic acid to the equimolar mixture of two compounds, 9,10,13- trihydroxy-11 (E)-octadecenoic acid (9,10,13-THOD) and 9,12,13-trihydroxy-10(E)-octadecenoic acid (9,12,13-THOD) which showed anti-fungal activities (Kim. H. Gardner. H.W., Hou, C.T., J. Ind. Microbiol. Biotechnol. 2000. 25, 109-115). In this study we report for the first time the effect of several Metal ions as catalytic agents of lipid peroxidation on the production of total THODs by PR3. Among eight different metal ions tested. Fe+2 and Cu+2 were effective to produce THODs. However bacterial growth was not significantly affected by the existence of metal ions tested. Fe+2 ion requirement was specific to THOD production from linoleic acid but not to other incorporation of dihydroxyl group on oleic acid and ricinoleic acid by PR3.