Abstract: To investigate the effect of nucleoside diphosphate kinase (NDK) on the synthesis of hyaluronic acid, nucleoside diphosphate kinase gene (ndk) was overexpressed along with the hyaluronic acid-producing genes in recombinant B.subtilis. Two engineered strains named Hp8tg and Pn8tg were constructed.Uniform hyaluronic acid (HA) could be obtained from both engineered strains.HA produced by both recombinant strains was confirmed by monosaccharide composition analysis, Fourier transform infrared spectometry and nuclear magnetic resonance spectroscopy.Inducing conditions of HA fermentation were optimized by response surface methodology.Overexpression of ndk could increase the production and molecular weight of HA by 1.3-fold and 1.1-fold, respectively. This study revealed for the first time that overexpression of ndk could relieve the inhibition effect of uridine diphosphate (UDP) on Class II HA synthase and increase the production and molecular weight of HA, which proves to be an efficient strategy for the production of HA, and the preparation of other polysaccharides.