Benthic ecology of certain selected seasonal and perennial prawn culture fields in the Cochin Backwater was studied for understanding the environmental factors controlling the abundance of the major groups of macrobenthos which form significant component of food of prawns. Substratum characteristics, bottom temperature, salinity, pH, oxygen. Eh and organic carbon content of the mud are the parameters examined for identifying the governing factors controlling the benthic abimdance in the areas investigated. Areas of high benthic abimdance are characterised by substratum comprising fine sand, silt and clay with not less than 20% fine sand. Only in area 3 the multiple regression model for predicting total biomass based on sand, silt, clay, organic matter and salinity was found to be significant explaining about 79 % of the variability. Sand, clay and silt were found to be relatively important factors controlling the benthic biomass. However, seasonal fluctuations of the substratum characteristics were foimd to influence the qualitative and quantitative composition of the biota in areas 1, 2 and 4. In all the areas of the seasonal and perennial ponds, almost all the groups, particularly the most dominant ones, viz. polychaetes, amphipods and tanaidaceans were correlated with sand and clay, but negatively with silt. Generally the benthos showed little coexistence; rather they preferred indepedent existence. None of the areas showed significant positive correlation between groups, r <0.632. Species diversity and biomass in the distribution showed much seasonal variations. Area 2 appeared to be more productive and rich in distribution compared to the rest of the areas.