CTD (conductivity, temperature and depth) data collected in the coastal waters of Rudsar in summer 2008 were analyzed to identify the isothermal layers, thermocline depth and vertical structure of seawater properties. During the survey, probe was released into the seawater column down to 117 m depth. Results showed a vertical variation of temperature between 29°C at the sea surface and less than 8°C at 117 m depth. In the southern coastal waters of the Caspian Sea, stratification process of seawater is completed in mid summer. In time of measurements, a strong thermocline was present between 10 m and 40 m depths with 18°C temperature decrease across it. Below thermocline, the temperature gradually decreased and reached less than 8°C at 117 m depth. Vertical and horizontal distributions of salinity were mainly between 12.18 psu and 13.1 psu. Density variations were in agreement with the temperature changes and the variations of density in the study area were between 1005.8 kg/m3 in the sea surface and 1010.4 kg/m3 near the bottom.