Caspian Sea as the largest lake in the world is an important based on ecological and economic issues. Recently, ecological events such as algal bloom in this region has been increased the importance of the study on the distribution and concentration of chlorophyll a . The chlorophyll a as a proxy of phytoplankton biomass has fundamental importance in biological and water quality studies. This study was focused on the distribution and concentration of chlorophyll a in the southern coast of Caspian Sea. The amount of chlorophyll a and traarency was investigated using field measurements and remote-sensing (RS) technique. Sampling was performed in different areas of the southern coast of Caspian Sea during different seasons (spring, summer, and fall). The results of the field data in spring showed that the minimum of chlorophyll a was obtained in the east, and the maximum was in the west area of southern Caspian Sea. The data also showed that maximum amount of the chlorophyll a was observed in Amirabad in fall, and minimum was in summer. The results of MODIS and IRS satellites showed that the amount of chlorophyll a incresed while the traarency decreased from east to west part of the southern coast of Caspian Sea which was probably due to an increasing of organic matter loading. The images also showed that the maximum amount of chlorophyll a was in Amirabad area during the fall which was in good agreement with the data obtained from field study. This study showed that in the MODIS satellite, band 2 has higher resolution and accuracy in measuring and distribution of chlorophyll a with compared to band 1. The results of this study showed that the satellite imagery followed with a field data is a usuful tool for ecological and biological changes such as distribution and amount of chlorophyll a in the Caspian Sea. Keywords: Chlorophyll a , Traarency, Satellite, Remote Sensing, Caspian Sea, Iran