In this research, bioaccumulation ability of seaweed species Ulva intestinalis and Sargassum angustifolium to heavy metals (Ni, Cd, Cu and Pb) and possible use of their chlorophylls content as biomarker of metals stress was studied. Samples of seaweeds and sediment were collected from four stations along the province of Bushehr coastal areas during January 2008 and June 2009. Chlorophylls of seaweeds were extracted using aceton (90%) and content of chlorophylls were determined spectrophotometrically. Metals in sediment and seaweeds were extracted using hot concentrated nitric acid (65%) and analysed by atomic absorption spectrophotometery. The mean concentrations of Ni, Cd, Cu, Pb in sediment were 32.17, 6.38, 6.90, 45.96 µg/g dry weight, in U. intestinalis 29.28, 4.08, 6.78, 32.08 µg/g dry weight, and in S. angustifolium 15.00, 3.78, 5.13 and 18.30 µg/g dry weight, respectively. Pearson correlation coefficients between metals in sediment and seaweeds showed significant correlation between Pb in sediment and U. intestinals and Cd and Pb in sediment and S. angustifolium. The results revealed, variations of Chlorophylls content in S. angustifolium has been shown to be a better indicator of environmental stress compare to U. intestinalis
