Specialized proresolving mediators (SPMs), such as resolvins and maresins, resolve inflammation and protect against infection at trace amounts generated by neutrophils and macrophages in humans. Thus, SPMs have been leading compounds in treatment of inflammation and infection. These mediators have been synthesized using chemical methods, which have disadvantages such as use of toxic chemical reagents, many (20–30) step reactions, and expensive processes. Here, we first discovered a human SPM-producing microorganism and found a 15-lipoxygenase (15-LOX) from the microorganism that produces SPMs via double oxygenation from polyunsaturated fatty acids. The 15-LOX was altered to 12-LOX using structure-based engineering. We performed the quantitative biocatalytic synthesis of SPMs by wild-type 15-LOX and engineered 12-LOX. Owing to the high double-oxygenating activities of LOXs, we succeeded in the one-enzyme biotransformation of docosahexaenoic acid and docosapentaenoic acid into the SPM resolvin D5 (RvD5, 7S,17S-dihydroxydocosahexaenoic acid) and RvD5n–3 DPA (7S,17S-dihydroxydocosapentaenoic acid) (40% conversion), respectively, by Escherichia coli expressing wild-type 15-LOX and into the 7S-epimer of maresin (MaR) 1 (7S,14S-dihydroxydocosahexaenoic acid) and 7S-epimer of MaR1n–3 DPA (7S,14S-dihydroxydocosapentaenoic acid) (20% conversion), respectively, by E. coli expressing engineered 12-LOX. Our study contributes to the environmentally friendly synthesis of medicinally important SPMs.