Immense quantity of waste is generated in association with poultry meat egg and crop production. The potential risks due to disposal of these wastes are magnified as a result of dense refinement of poultry production and the decreasing amount of land available for waste disposal. The study aims at studying the microbiological biodiversity of poultry waste and paddy straw based co-composting system. The predominant microflora of the poultry manure were bacteria, fungi, enteric bacteria and spore forming bacteria whose population was high at the initiation of composting but decreased significantly as the compost approached maturity. The initial load of inherent enteric groups of bacteria in poultry waste, that also includes some pathogenic ones, is considerably reduced and some new vital groups contributed to compost quality as the microbiological biodiversity sets in the system and becomes stable. Major fraction of nitrogen of poultry waste was subjected to ammonia volatilization and a fraction of it conserved by cocomposting it in conjunction with wastes having low nitrogen contents. In the treatment T 1 and T 5 , where poultry manure and paddy straws alone were composted, 60 and 30 percent of organic carbon, respectively, was lost over a period of six months. Whereas in treatments T 2 ,T 3 and T 4, poultry manure and paddy straw were co-composted in the ratio of 3:1, 2:2 and 1:3, respectively, 51.4,45.0 and 37.0 percent of carbon, respectively, was lost during decomposition. The C: N ratio in all the treatments decreased significantly to 18.3 for T 1 , 24.7 for T 2 , 27.0 for T 3 , 34.9 for T 4 and 38.5 for T 5 at the end of composting period.