Abstract: The study focused on effects of seawater pollution on total count, distribution and size of the species Ammonia beccarii through studying the effect of some parameters i.e. Biochemical Oxygen Demand (BOD) and seasonal variation on two locations of Gaza Strip Seashore line. The results showed that in the polluted site the TC change was closer with increase or decrease of BOD5. In free site, with low concentrations of BOD5 (no pollution) the TC was more affected by sampling time. The size of the organism was affected relatively in winter season in the polluted site as temperature and related biochemical activities decreased. The low average size in polluted site was higher than the highest average size of free site. The size of Ammonia beccarii was better indicator for organic pollution level in comparison to total count.