A gram-negative, motile, coccoid- and amorphous-shaped, non-pigmented chemoheterotrophic bacterium, designated strain PZ-5(T), was isolated from sea water of Sagami Bay in Japan and subjected to a polyphasic taxonomic study. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the novel isolate could be affiliated with the class Gammaproteobacteria. Strain PZ-5(T) showed below 93.9% similarity with validly published bacteria and demonstrated the highest sequence similarity to Dasania marina KOPRI 20902(T) (93.9%). Strain PZ-5(T) formed a monophyletic group with D. marina KOPRI 20902(T). The DNA G+C content of strain PZ-5(T) was 49.8 mol%. The major isoprenoid quinone was Q-8 and predominant cellular fatty acids were C(15:0) ISO 2OH (19%), C(16:1) omega 7c (17.4%), C(17:1) omega 8c (16.2%), C(11:0) 3OH (7.5%), and C(15:1) omega 8c (6.5%). Based on evidence from a polyphasic taxonomical study, it was concluded that the strain should be classified as representing a new genus and species of the class Gammaproteobacteria, for which the name Oceanicoccus sagamiensis gen. nov., sp. nov., (type strain PZ-5(T) =NBRC 107125(T) =KCTC 23278(T)) is proposed.