A novel facultative anaerobic, Gram-stain-positive coccus, strain JS71(T), was isolated from the human subgingival dental plaque of a periodontitis lesion. Phylogenetic analysis based on the 16S ribosomal RNA gene (16S rDNA) revealed that the strain belonged to the genus Streptococcus. The 16S rDNA sequence had high similarity with Streptococcus rubneri DSM 26920(T) (98.6%), Streptococcus parasanguinis ATCC 15912(T) (98.5%), and Streptococcus australis CCUG 45919(T) (98.3%). The genome of strain JS71(T) was 2,009,592 bp in length. The DNA G+C content of the strain was 42.1 mol%. Average nucleotide identity values between strain JS71(T) and S. rubneri DSM 26920(T), S. parasanguinis ATCC 15912(T), and S. australis CCUG 45919(T) were 88.9%, 80.8%, and 92.4%, respectively. Genome-to-genome distance values between strain JS71(T) S. rubneri DSM 26920(T), S. parasanguinis ATCC 15912(T), and S. australis CCUG 45919(T) were 36.5% (34-39%), 26.3% (23.9-28.7%), and 48.0% (45.4-50.6%), respectively. The major fatty acids of the strain were C-16:0 (39.7%), C-18:1 omega 6c/C-18:1 omega 7c (15.5%), and C-18:0 (10.4%). Based on these results, strain JS71(T) (= KCOM -2890(T) = JCM -33454(T)) should be a novel species of the genus Streptococcus, for which the name Streptococcus koreensis sp. nov. is proposed.