Structures of seawater properties in the southern continental shelf of the Caspian Sea, off Babolsar were investigated. In November, water temperature was around 18°C at the sea surface and reached to about 9°C at 42 m depth. A seasonal thermocline observed below 30 m depth with more than 8°C temperature gradient across it. High concentrations of chlorophyll-a were observed in subsurface layer (at depth of 15 m) in the region. Vertical gradient of the sound speed across the thermocline was more than surface mixed layer. Variations of density and sound velocity in the coastal waters of the sea were in agreement with temperature changes.