An agarolytic bacterium, designated as strain M5c(T), was isolated from sea sand in Jeju Island, Korea. This isolate was Gram-negative, positive for catalase and oxidase, rod and motile by means of monotrichous flagella. Strain M5c(T) has translucent or dark ivory colonies, forms a dent on an agar plate under colonies, and grows in the presence of 1-12% (w/v) NaCl and at 10-37°C. This isolate hydrolyzes agar, alginic acid, carboxymethyl (CM)-cellulose and starch. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain M5c(T) can be considered as a species within the genus Gilvimarinus, being most closely related to Gilvimarinus chinensis QM42(T), with a 16S rRNA gene sequence similarity of 95.6%. The major cellular fatty acids were C16:1?7c and/or iso-C15:0 2OH (33.5%), C16:0 (26.5%) and C18:1?7c (14.1%). The DNA G+C content was 53.8 mol%. Based on these polyphasic data, strain M5c(T) should be classified as a novel species, for which the name Gilvimarinus agarilyticus sp. nov. is proposed. The type strain for the novel species is M5c(T) (= KCTC 23325(T) = NCAIM B 02425(T)).