Atopic dermatitis (AD) is a chronic skin disease characterized by inflammation, pruritus, and eczematous lesions. Recently, sacran, a new polysaccharide isolated from cyanobacterium Aphanothece sacrum (Sur.) OKADA discovered by Suringar in the 19th century, has received considerable attention as a novel biomaterial. Previously, it was reported that sacran exhibits potent anti-inflammatory effects for skin diseases produced by various stimulants with optimum effective concentrations at 0.01% (w/v) and 0.05% (w/v) in rats and mice. Importantly, we demonstrated clinically that almost all of the average scores for AD symptoms in patient treated with sacran solutions were improved. In AD model mice, sacran treatment markedly down-regulated inflammatory cytokine and chemokine mRNA levels compared with non-treated controls. Furthermore, sacran solution significantly suppressed inflammation response in RAW264.7 cells. In RBL-2H3 cells, the sacran solution significantly lowered degranulation. Taken together, our studies suggest sacran may have the potential to improve AD through functional recovery of skin barrier and anti-inflammatory effects.