Heavy metals are not biodegradable and can accumulate in living tissues along the food chain, reaching humans mainly through food. Crabs and other organisms that feed on organic matter in estuarine ecosystem can absorb a greater burden of these toxic elements and thus pose a potential risk to the health of the region's population. Blue crabs collected along three estuaries of the Arabian Gulf. In this work, Measurement of water temperature in ο C , salinity g/l, conductivity in Siemens per meter (S/m), water turbidity in NTU, total hardness g/l, water PH in mg/l and water dissolved oxygen in mg/l were measured by a probe HORIBA ® mod. U-22/Water Quality-Checker [1]. Quantitative studies were carried out on Cu, Zn, Cd, Pb, Cr, Al , Fe, Mn and Ni content in sea water and in the gills of the blue crab Portunus pelagicus (n = 480). Analysis of heavy metals was performed by energy dispersive x-ray fluorescence (EDXRF). Values of salinity g/l, conductivity in Siemens per meter (S/m), water turbidity in NTU, total hardness g/l and water PH in mg/l are within the recommended range CONAMA Resolution No. 357/2005 European Union standards [2], Saudi Arabian Standards [3], WHO [4]. Collected data show that crabs live in Southern Khobar estuary contain