A biocompatible, heterogeneous, fucose-rich, sulfated polysaccharide (fucoidan) is biosynthesized in brown seaweed. In this study, fucoidan was isolated from (PAC) using celluclast-assisted extraction, purified, and evaluated for its anti-inflammatory potential in lipopolysaccharide (LPS)-induced RAW 264.7 cells. Structural analyses were performed using Fourier transform infrared (FTIR) and scanning electron microscopy. Among the purified fucoidans, fucoidan fraction 5 (F5) exhibited strong inhibitory activity against LPS-induced nitric oxide (NO) production and pro-inflammatory cytokine generation through the regulation of iNOS/COX-2, MAPK, and NF-κB signaling in LPS-induced RAW 264.7 cells. Determination of the structural characteristics indicated that purified F5 exhibited characteristics similar to those of commercial fucoidan. In addition, further analyses suggested that F5 inhibits LPS-induced toxicity, cell death, and NO generation in zebrafish models. Taken together, these findings imply that fucoidans have exceptional anti-inflammatory action, both in vitro and in vivo, and that they may have prospective uses in the functional food sector.