The study is part of a research project on the southern shores of the Caspian Sea (Mazandaran waters- Kelarabad) was conducted in 2012. The aim of this study was to evaluate the effects of fish farming in cages on the distribution, abundance and biomass of macrobenthos organisms in the water at a depth of 20 meters Kelarabad. Sampling was monthly at three stations including 1(seating cage), 2 (control with a distance of 500 m) and 3 (50 meters after the cage) using a grab with 30 cm diameter. A total of 6 groups of benthic organisms, including 2 branches, 2classes, 4 families and 6 species were identified. Overall, 23442 specimens of large benthic organisms were counted, the lowest and highest frequency at stations 1 (23.4%) and 2 (46.8%), respectively. The results showed that the highest abundance at station 2 with an average of 646.00±1230.43 N/m² and biomass with 0.526±1.00 g/m² in station 3, in which can be due to the lack of cage fish farming activity and the presence of big species to depend Cerastoderma lamarki, respectively. The highest abundance and biomass was in autumn with mean 888.3±1371.58 N/m² and 0.524±0.887 g/m² and lowest was in winter with mean 143.33±138.22 N/m² and 0.070±0.078 g/m². This could be related to activity fish cage culture and wintering season. The Streblospio gynobranchiata of polychaeta dominant benthic organisms with large population accounted 93.3%. This could be due to exotic species, high power compatibility and suitability related to environmental conditions. The conclusion is that the abundance and biomass of macrobenthos organisms in station 1 was less than other stations in which can be duo to concerned fish cage activity and its effects on organisms’ infauna. Therefore, it is suggested that any activity in the Caspian Sea offshore aquaculture should maintain environmental considerations and implementation of detailed environmental impact assessment (EIA) projects.