Hyaluronic acid (HA) is an important material for medical, cosmetic and food applications. HA is obtained commercially from rooster combs and the fermentation of streptococci. However, the safety problems such as hyaluronidase or exotoxin contamination remain controversial. To reduce the risk of hyaluronidase or exotoxin contamination, we attempted to isolate strains of Streptococcus thermophilus with high productivity of useful exopolysaccharides (EPSs) including HA from traditional dairy food products. Forty-six S. thermophilus strains were isolated from dairy food products, and examined of their HA production using a HA binding protein method. According to the results, six S. thermophilus strains produced EPSs including HA. S. thermophilus YIT 2084 had a markedly high HA productivity (approximately 8 mg/l). We focused on the high-molecular-mass fraction of EPS (2000 kDa) from S. thermophilus YIT 2084. By using high-performance liquid chromatography, it was found that a high-molecular-mass fraction of EPS included N-acetylglucosamine (54.4%) and glucuronic acid (45.6%), which are components of HA. Furthermore, 13C-nuclear magnetic resonance spectroscopy showed that the spectra of the high-molecular-mass fraction corresponded well to those of commercial HA. Here, we described for the first time that S. thermophilus, which is a generally recognized safe bacterium, produces HA. The novel HA-producing bacterium S thermophilus YIT 2084 has great potential for applications in the medical, cosmetic and food fields, although its culture conditions remain to be improved.