Investigation on the degradation of pyrazosulfuron ethyl by Aspergillus terreus in the rice ecosystem was conducted at the Department of Biochemistry, UBKV, Pundibari Coochbehar, West Bengal, India. The soil was collected from the paddy field to isolate fungal inoculums. Results revealed that Aspergillus terreus can survive in minimal broth containing pyrazosulfuron ethyl at 1000 ppm and degrades through two major pathways, first involves the cleaves of sulfonylurea bridge resulting in the formation of two major metabolites viz., 2-amino-4, 6 –dimethoxyprimidine, 5-aminosulfonyl-1-methyl-pyrazole-4-carboxylic ethyl ester and, second was the cleavage of sulfonyl amide linkage which forms the metabolite viz; 1 methyl pyrazole-4-carboxylic acid ethyl ester,1 methyl pyrazole -4-carboxylic acid, 5-carbamoyl -1-methyl pyrazole -4-carboxylic acid ethyl-ester. The enzyme involved in these transformations can be utilized to decontaminate soil and water from Pyrazosulfuron ethyl residue. Even, the gene responsible for the production of these useful enzymes can be exploited for future research.