Two non-motile, orange- or yellow-pigmented bacteria, designated strains KYW48(T) and KYW147(T), were isolated from seawater collected from the South Sea, Republic of Korea. Cells of both strains were Gram-reaction-negative, aerobic and catalase- and oxidase-positive. The major fatty acids of strain KYW48(T) were C(18 : 1)ω7c (35.3 %), summed feature 3 (iso-C(15 : 0) 2-OH and/or C(16 : 1)ω7c) (22.7 %), C(17 : 1)ω6c (19.8 %), C(14 : 0) 2-OH (7.4 %) and C(16 : 0) (5.9 %), and those of strain KYW147(T) were C(18 : 1)ω7c (36.0 %), summed feature 3 (18.3 %), C(16 : 0) (14.7 %), 11-methyl C(18 : 1)ω7c (10.7 %), C(16 : 0) 2-OH (9.1 %) and C(18 : 1)ω9c (8.0 %). The predominant isoprenoid quinone of both strains was ubiquinone 10 (Q-10). The DNA G+C contents of strains KYW48(T) and KYW147(T) were 63.8 and 67.2 mol%, respectively. A phylogenetic tree based on 16S rRNA gene sequences showed that strains KYW48(T) and KYW147(T) were grouped with the members of the family Erythrobacteraceae and formed a distinct clade with the members of the genus Altererythrobacter (<95.7 % sequence similarity). On the basis of the evidence presented in this study, the novel species Altererythrobacter namhicola sp. nov. (type strain KYW48(T) = KCTC 22736(T) = JCM 16345(T)) and Altererythrobacter aestuarii sp. nov. (type strain KYW147(T) = KCTC 22735(T) = JCM 16339(T)) are proposed.