Fucoidan, a sulfated polysaccharide present in marine brown seaweed, has been demonstrated to inhibit in vivo and in vitro growth of cells. The present study was conducted in HT‑29 human colon cancer cells cultured at a high density, and examined the potential underlying mechanisms by which fucoidan exerts its anti‑proliferative effects, which remain poorly understood. Fucoidan treatment of high‑density HT‑29 cells resulted in the inhibition of cell growth and increased apoptotic cell death. Flow cytometric analysis revealed that fucoidan treatment led to sub‑G1 phase cell cycle arrest. This was associated with decreased protein expression levels of Retinoblastoma protein and E2 factor protein. In conclusion, the results of the present study demonstrated that fucoidan possesses anticancer activity against high density HT‑29 cells by inhibiting cell growth and cell cycle progression.