Fenugreek is a dietary supplement for anti-aging and human health. (2S, 3R, 4S)-4-hydroxyisoleucine (4-HIL), which is extracted from fenugreek seeds, is expected to be a promising orally active drug for diabetes and diabetic nephropathy because of its insulinotropic effect. Although several chemical synthesis methods of 4-HIL have been proposed, these methods require multistep reactions to control the stereochemistry of 4-HIL. In this study, we modified the key enzyme 4-HIL dehydrogenase (HILDH) to overcome the biggest limitation in commercial-scale production of 4-HIL. As a result, an effective one-step carbonyl reduction to produce (2S, 3R, 4S)-4-HIL was successfully accomplished with strict stereoselectivity (>99% de). Mass production of (2S, 3R, 4S)-4-HIL by our synthetic method could have a significant contribution to the prevention of diabetes, dyslipidemia, and Alzheimer's disease. (120 words/200 words)