Hyaluronic acid (HA) is a linear and negatively charged polysaccharide regularly used in medicine and cosmetics. Recently, Streptococcus zooepidemicus has been exploited in the fermentation industry to produce HA. Many studies showed that higher amounts of HA were produced under aerobic condition compared with anaerobic conditions. In order to explore the effect of oxygen on the HA synthesis in S. zooepidemicus, 2-DE was used to compare the proteomes of aerobically and anaerobically fermented bacteria to identify proteins, which might be associated with the influence of oxygen on the HA synthesis. Totally nine pairs of 2-DE gels collected from three batches were compared and nine over-expressed proteins were observed in aerobically fermented bacteria. These proteins were identified by LC-MS/MS as dihydrolipoamide dehydrogenase, UDP-acetyl-glucosamine pyrophosphoylase, dihydrolipoamide-S-acetyltransferase, and acetoin dehydrogenase α and β chains, respectively. These up-regulated proteins were involved in acetoin dissimilation, the central carbon metabolism, and the HA anabolic pathway, implicating that oxygen might augment the expression of genes that are involved in central energy metabolism, acetoin reutilization, and HA biosynthesis to enhance the amount of acetyl-CoA as such more acetyl-CoA can be divergent from the central carbon metabolism to replenish acetyl-CoA for the HA synthesis.