Atopic dermatitis (AD) is a chronic inflammatory and pruritic disease; it can be treated by inhibiting inflammation. Sarcodia suiaesp. is an edible, artificially cultivable red algae with multiple bioactivities. We assessed the anti-inflammatory activity of the ethyl acetate fraction of S. suiaesp. ethanol extract (PD1) on 1-chloro-2,4-dinitrochlorobenzene (DNCB)-induced AD-like lesions. Results show that PD1 alleviated symptoms and significantly decreased clinical dermatitis score. PD1 inhibited serum immunoglobulin E expression and alleviated swelling in the spleen and subiliac lymph nodes. In skin tissues, PD1 alleviated aberrant hyperplasia, decreased epidermal thickness, and decreased the accumulation of mast cells. PD1 mediated the recovery of skin barrier-related proteins, such as claudin-1 and filaggrin. Our study demonstrated that PD1 has anti-inflammatory effects, alleviates AD symptoms, inhibits inflammatory responses in skin tissues, and restores barrier function in DNCB-induced AD mice. These findings reveal that S. suiaesp. extract provides an alternative protective option against AD.Graphical AbstractA cultured red macroalgae (Sarcodia suiae sp.) extract alleviates skin inflammatory responses and barrier dysfunctions in atopic dermatitis.