The dominant molluscan species Patella caerulea was selected as a trace metals bio indicator. During winter and summer 2016, its specimens were scraped from El-Mex Bay. Concentrations of heavy metals in the water, sediments and Patella caerulea (shells and soft tissues) were determined. Cadmium (Cd), lead (Pb), copper (Cu), iron (Fe), nickel (Ni), manganese (Mn) and zinc (Zn) concentrations (conc.) during summer were higher than winter except for shells which had Cd conc. in summer lower than winter, water showed Cu conc. in winter more than summer, Fe appeared higher conc. in water and Patella caerulea during winter more than summer, Mn had higher conc. in water and sediments than summer, Ni had higher conc. in water and soft tissues during winter than summer and Zn in water during summer is lower than winter. The bioaccumulation factors (BAFs) of Cd, Pb, Cu, Fe in Patella caerulea shells were more than soft tissues, also they were more in winter than summer except that of Cu in winter was lower than summer, BAF of Fe in soft tissues was higher than shells also that of Mn and Zn in Patella caerulea during winter were lower than summer, also BAFs of Mn in soft tissues and shells was nearly similar. The highest metal pollution index (MPI) for the studied species appeared in shells (105.95) followed by that of soft tissues during summer and winter (80.54 and 74.64, respectively). While MPI in shells during winter (46.13) came to the last. [ABSTRACT FROM AUTHOR]