Psychrophilic bacteria, which grow on lactose as a carbon source, were isolated from Antarctic polar sea water. Among the psychrophilic bacteria isolated, strain KNOUC808 was able to grow on lactose at below 5ºC, and showed 0.867 unit of o-nitrophenyl β-D-galactopyranoside(ONPG) hydrolyzing activity at 4ºC. The isolate was gram-negative, rod, aerobic, catalase positive and oxidase positive. Optimum growth was done at 20ºC, pH 6.8-7.2. The composition of major fatty acids in cell of KNOUC801 was C12:0 (5.48%), C12:0 3OH (9.21%), C16:0 (41.83%), C17:0 ω8 (7.24%) and C18:1 ω7 (7.04%). All suthese results together suggest that it is affiliated with Pseudoalteromonas genus. The 16S rDNA sequence corroborate the phenotypic tests and the novel strain was designated as Pseudoalteromonas sp. KNOUC808. The optimum temperature and pH for lactose hydrolyzing enzyme was 20ºC and 7.8, respectively. The enzyme was stable at 4ºC for 7 days, but its activity decreased to about 50% of initial activity at 37ºC in 7 days.