The aim of this study was to understand spatial and temporal variations of inorganic and organic forms of phosphorus in the surface and deep waters of Erdemli shelf zone of the Mersin Bay. For this goal, time-series hydrographical and phosphorus data were obtained monthly at the three selected stations between December 2001 and December 2003. The present results have shown that the concentrations of different fractions of total phosphorus displayed a decreasing trend from nearshore to shelfbreak zone of the bay. Total phosphorus (dissolved+particulate) in the shelf water was dominated by dissolved-P fraction (TDP:56-97%) and dissolved organic-P (DOP) was principally the major constituent of the TDP in the shelf water. Similarly, particulate organic-P (POP) dominates the particulate-P (PP) pool; however, the contribution of particulate inorganic-P (PIP) to PP pool was more pronounced in the nearshore zone fed by riverine inputs.