Aims This study aims to produce hydroxy fatty acids efficiently. Methods and Results Escherichia coli overexpressing linoleic acid Delta9 hydratase from Lactobacillus plantarum AKU 1009a was employed to produce hydroxy fatty acids with industrial potential. We found that 280 g l-1 of linoleic acid (1 mol l-1) was converted into (S)-10-hydoxy-cis-12-octadecenoic acid (HYA) with a high conversion rate of 98% (mol/mol) and more than 99·9% enantiomeric excess (e.e.) by recombinant E. coli cells in the presence of FAD and NADH. In the same way, many kinds of C18 unsaturated fatty acids with Delta9 carbon double bond (280 g l-1) were converted into corresponding 10-hydroxy fatty acids with the conversion rates over 95% (mol/mol). We also produced HYA at a high rate of accumulation (289 g l-1) with a high yield (97 mol%) in a reaction mixture that contained glucose instead of NADH. Conclusions We developed a process for producing several types of hydroxy fatty acids with high accumulation rates and high yields. Significance and Impact of the Study Hydroxy fatty acids are important materials for the chemical, food, cosmetic and pharmaceutical industries, and thus they have recently attracted much interest in a variety of research fields. However, the mass production of hydroxy fatty acids has been limited. This method of hydroxy fatty acids production will facilitate the widespread application of hydroxy fatty acids in various industries.