Seaweeds are good bio-monitors of heavy metal pollution and have been included in European coastal monitoring programs. However, data for seaweed species in China are scarce or missing. In this study, we explored the potential of seaweeds as bio-monitor by screening the natural occurring seaweeds in the “Kingdom of seaweed and shellfish” at Dongtou Islands, the East China Sea. Totally, 12 seaweed species were collected from six sites, with richness following the sequence of Rhodophyta > Phaeophyta > Chlorophyta. The concentration of heavy metals (Cu, Cr, Ni, Zn, Pb, Cd, As) in the seaweeds was determined, and the bioaccumulation coefficient was calculated. A combination of four seaweeds, Pachydictyon coriaceum, Gelidium divaricatum, Sargassum thunbergii, and Pterocladiella capillacea, were proposed as bio-monitors due to their high bioaccumulation capabilities of specific heavy metals in the East China Sea and hence hinted the importance of using seaweed community for monitoring of pollution rather than single species. Our results provide first-hand data for the selection of bio-monitor species for heavy metals in the East China Sea and contribute to selection of cosmopolitan bio-monitor communities over geographical large area, which will benefit the establishment of monitoring programs for coastal heavy metal contamination.