Technical Abstract: Hydroxy fatty acids (HFA), originally found in small amounts mainly from plant systems, are well known to have special properties such as higher viscosity and reactivity compared with other normal fatty acids. These special properties make HFAs have high industrial potentials in a wide range of applications including resins, waxes, nylons, plastics, lubricants, cosmetics, and antimicrobial agents. Recently, various microbial strains were tested to produce HFAs from different unsaturated fatty acids. Among those microbial strains tested, Pseudomonas aeruginosa PR3 (NRRL B-18602) are well known to utilize various unsaturated fatty acids to produce mono-, di-, and trihydroxy fatty acids. Previously we reported that strain PR3 could utilize triolein as a substrate for the production of 7,10-dihydroxy-8(E)-octadecenoic acid (DOD) via the induction of lipase activity (Chang IA, Kim IH, Kang SC, Hou CT, Kim HR 2007, Appl Microbiol Biotechnol 74:301-306). In this study, we focused on development of the optimal environmental conditions for DOD production from triolein by PR3. Optimal initial medium pH and incubation temperature were pH 8.0 and 25oC, respectively. The Magnesium ion was essentially required for DOD production. Other important conditions including inoculum size, time for substrate addition, substrate concentration were also studied.