A novel facultative anaerobic, non-spore forming, non-motile, and Gram-stain-positive coccus, designated strain ChDC B353(T), was isolated from human postoperative maxillary cyst. The 16S ribosomal RNA gene (16S rDNA) sequence of the strain was most closely related to those of Streptococcus pseudopneumoniae ATCC BAA-960(T) (99.4%), Streptococcus mitis NCTC 12261(T) (99.3%), and Streptococcus pneumoniae NCTC 7465(T) (99.2%). The major fatty acids of the strain were C-16:0 (43.2%) and C-18:1 omega 6c/C-18:1 omega 7c (20.2%). The genome of strain ChDC B353(T) was composed of 1,902,053 bps. The DNA G+C content of the strain was 40.2 mol%. Average nucleotide identity (ANI) values between strain ChDC B353(T) and S. pseudopneumoniae ATCC BAA-960(T), S. mitis NCTC 12261(T), and S. pneumoniae NCTC 7465(T) were 91.9%, 93.5%, and 91.3%, respectively. Genome-to-genome distance (GGD) values between strain ChDC B353(T) and S. pseudopneumoniae ATCC BAA-960(T), S. mitis NCTC 12261(T), or S. pneumoniae NCTC 7465(T) were 46.6% (44.0-49.2%), 53.2% (50.5-55.9%), and 46.0% (43.5-48.7%), respectively. The threshold values of ANI and GGD for species discrimination are 95-96% and 70%, respectively. These results reveal that strain ChDC B353(T) (= KCOM 1699(T) = JCM 33453(T)) is a novel species belonging to genus Streptococcus, for which a name of Streptococcus chosunense sp. nov. is proposed.