To produce high-, medium- and low-molecular-weight hyaluronic acid (HA) at different temperatures using engineeredBacillus subtilisexpressing hyaluronidase (HAase) from leech. By overexpressing the HAase genehyain the HA-producing strain WmB using temperature-sensitive plasmid pKSV7, the engineered strain WmB-PYh produced HA with different molecular weights (8.61 kDa at 32 degrees C, 0.615 MDa at 42 degrees C, and 6.19 MDa at 47 degrees C). In this study, the molecular weight of HA was regulated by using leech HAase expressed from a temperature-sensitive plasmid. We thus obtained different molecular weight HAs by using a single bacterial strain at different culture temperatures.