Seasonal variations of the seawater properties (e.g. temperature, salinity, density and chlorophyll-a) in western part of the southern coastal waters of the Caspian Sea near the Iranian coast were studied. A portable CTD probe was applied for profiling from sea surface to bottom at 23 stations. Maximum depth of the profiling stations was more than 470 m in the study area. Vertical structure of temperature in the southern Caspian Sea waters is characterized by a significant seasonal thermocline between 20-50 m depths in summer with a vertical gradient of 16 oC. Seasonal average of the salinity was in a range of 12.27-12.37 PSU in period of measurements. The data showed that the most chlorophyll-a was found below the sea surface. In general, variations of the chlorophyll-a concentration in the study area can be attributed to the effect of changes of seawater characteristics in various seasons, stratification and heating the sea surface layer in the warm seasons and discharge of lagoon and rivers in the study area. The range of the concentrations at the sea surface in August and November were higher than the measured values in April in the study area. Concentrations of chlorophyll-a were recorded in midsummer in a range of 0.2-3.4 mg m-3.