Hyaluronic acid (HA) production was metabolically engineered in Lactococcus lactis by introducing the HA synthetic machinery from the has operon of the pathogenic bacterium Streptococcus zooepidemicus. This study shows that the insertion of uridine diphosphate (UDP)-glucose pyrophosphorylase (hasC) gene in addition to the HA synthase (hasA) and UDP-glucose dehydrogenase (hasB) genes has a significant impact on increasing HA production. The recombinant L. lactis NZ9000 strain transformed with the plasmid pSJR2 (co-expressing hasA and hasB genes only) produced a maximum of 107 mg/l HA in static flask experiments with varying initial glucose concentrations, while the corresponding experiments with the transformant SJR3 (co-expressing hasA, hasB, and hasC genes) gave a maximum yield of 234 mg/l HA. The plasmid cloned with the insertion of the full has operon comprising of five different genes (hasA, hasB, hasC, hasD, and hasE) exhibited structural instability. The HA yield was further enhanced in batch bioreactor experiments with controlled pH and aeration, and a maximum of 1.8 g/l HA was produced by the SJR3 culture.